hey n3rv, not sure about playing for free. Have never explored to see if can do play chips in heads up on any sites, however if able to play on FTP they have sng style headsup for 50c, which is a great way to get the experience without risking a great deal.
I would certainly be careful about any heads-up cash with your freind because lets say he decides to be a major donky, and not get lucky, then it could easily look like chip dumping with is something not taken lightly on many sites. At least with the heads up sng, you can do the regular speed with 1500 chips and have plenty of play heads up, they even have a deepstack with 3k chips but can't recall if those are in the 50c range.
Also might sometimes be a challenge to get on the same table, unless it is something like the deepstack which often don't fill too often as many players do the turbo or super turbo games. Just a thought, but if looking for a small buyin with some play would have to recommend ftp, again on the same note i havn't looking at real money
play on many sites besides pstars, ftp and titan (titan is also good as they have 10c, 20c 6max and 10person sng's, and cheap steps).