expression, pragmatic marker
as a parenthetical expression, marking a metaphorical rather than literal sense.
In the sentence "He's a sadist, if you will", the phrase signals that the speaker is acknowledging that the choice of words might be unfamiliar or novel to the audience in that particular context. The expression is likely derived from a clipping of a clause such as "if you will allow me to express my idea in these words".
The construction is identified in Brinton (2008: 164) as Canadian by frequency in comparison to UK data (see Chart 1). However, comparison with newspaper data from Canada, the UK and the US for 2009 and 2010 (Chart 2), reveals it as a predominantly North American construction that is no Canadianism as defined in the DCHP-2 typology. The data in Chart 2 is roughly equivalent to the three pragmatic meanings in Chart 1. There may be a chance that some sub meaning may reveal a national dimension, but our current data does not support such a claim. Brinton's data, which is based on the Strathy Corpus (to 2005), shows that parenthetical if you will “is more fully grammaticalized as a pragmatic marker in Canadian English than in British English” (Brinton 2008: 164). The American data suggests that the construction is most grammaticalized in the US, with Canada on its heels and Britain lagging behind.
- 1990  "I believe the intent is to modify and Canadianize it, if you will, for our own cultures and laws, and go it on our own," says board member Ald. Carol Kraychy. 
- 1998  Another, more common perception, or misconception if you will, is that this Inuk born in a sod house in 1957, typically shunted around from one government school to another, is just one more aboriginal with a video camera doing vaguely interesting ethnographic stuff. Filming scenes of igloos built and of seals butchered for food. Typically tedious hand-held footage with low-production values and of marginal interest to anyone south of 60.
The truth is that Kunuk's videos are amazing. Take for example Episode 4, Ice House, from Isuma's series of 13 half-hour dramas titled Nunavut. The series depicts life in a single very significant year -- 1945. This is when the government of Canada started to take over from religious missionaries in looking after the education and the health of the Inuit. 
- 2000  In 1851, he was party to the Treaty of Fort Laramie involving the U.S. government and several Indian tribes. And in 1855, he was party to a treaty with several Blackfoot tribes whose hunting territory included the upper Missouri and Yellowstone Rivers.
"As I read them, these paragraphs amount to an assertion by the band of a claim to international sovereignty and nationhood -- to international personhood, if you will," Hugesson ruled. 
- 2005  "As Governor General, I wanted to make a pilgrimage, if you will, to the very place where in 1864 the fathers of Confederation first set in motion the dream that is Canada, a dream that soon after became a reality," she said during a welcoming ceremony at Province House.
"It's a dream that we continue to shape with our own adventures, our own experiences, our own viewpoints, and, we must admit, the lessons we have learned from our mistakes."
Jean said she could almost hear the echoes from the past as she walked through the old P.E.I. legislature, where certain rooms have been kept largely unchanged since the fathers of Confederation debated and finally agreed upon the fundamentals of Canada. 
- 2007  I have a distinct memory of being loudly chastised with: "Campbell! We're not out here to watch you walk!" a situation made even more mortifying considering that I was actually a hyper-sensitive, conscientious kid who worked hard to please others. A keener, if you will. 
- 2011  The Boston band's first time through Victoria was a landmark event on the 2004 calendar; one for the history books, if you will. 
- 2016  Like the man himself, Cuba -- the Pearl of the Caribbean, a tiny developing nation with a population of barely 11 million -- was considered a country of enormous stature, a miniature superpower, if you will. Under Castro's leadership, Cuba not only talked big, but it acted big as well. 
Images:
Chart 1: Pragmatic marker if you will by function in British English (BNC) and Canadian English (Strathy) (source: Brinton 2008: 164)
Chart 2: Tokens of pragmatic if you will in The Globe and Mail, The London Times, and The New York Times in 2009 and 2010.