You're pretty much going to have to have a microphone. If you absolutely cannot
help rolling around in that chair I would suggest that you spend the money for a
wireless mic. Today's sound cards often use electrit type microphones hence
have power going to the mic. Even if you could use an earphone the sound
quality would be completely unacceptable.
Tom
Tom Brennan KD5VIJ, CCC-A/SLP
web page http://titan.sfasu.edu/~g_brennantg/sonicpage.html