It's true you can't change your personality, but you can sharpen your skills a little bit. I like the script idea some one suggested, I do the same thing. I can do ok for short period of times, but after awhile I run out of scripts. I like being around people for short period of times but then need to be alone.

And just for the record, no one is 100% INTROVERT or 100% EXTRAVERT. Such a person would be a lunatic