The only time I am aware of a Axl impersonator was on the 2004 Las Vegas show. He goes by the name of "Asshole Rose". He looks and sounds nothing like Axl. Asshole was playing a game of Hollyweird Squares against a dragqueen Tina Turner. The segment was only about a half an hour long. If I remember right Asshole got beat in the game... I dont know where you can get the audio from the show but you can watch E! for the replay. They are airing the 2004 Vegas trip this week. Here is the schedule.
December 27, 2004 to January 2, 2004 - E! Howard Stern Show Weekly Schedule
11:00 PM (and 2:00 AM exc. Sat.) 11:30 PM
Monday Las Vegas '04, Day 1 Show 1 (R) Las Vegas '04, Day 1 Show 2 (R)
Tuesday Las Vegas '04, Day 1 Show 3 (R) Las Vegas '04, Day 2 Show 1 (R)
Wednesday Las Vegas '04, Day 2 Show 2 (R) Las Vegas '04, Day 2 Show 3 (R)
Thursday Las Vegas '04, Day 2 Show 4 (R) Las Vegas '04, Day 2 Show 5 (R)
Friday Las Vegas '04, Day 3 Show 1 (R) Las Vegas '04, Day 3 Show 3 (R)
http://www.marksfriggin.com/e-show.htm