You are joking, right?
You've more chance of seeing Brown in a Morris Dancer's costume than a kilt! (After all, you would never guess our outgoing PM is a jock, would you?)
Brown already has a voice coach ironing out the brogue - every time he says "want" it comes out as "wunt", a la John Major.
But at least he's getting it easy - given the school Blair went to he probably had his accent beaten out of him.
PS If you don't already have a kilt or even a Clan connection - check out the following:
http://www.erskine.org.uk/tartan.asp