Originally Posted by Hags888

Depending on the note and the piece, sometimes you can get away with a false-fingering trill on a tremolo. So, if the note was a high G right above the staff, trilling open to 1-2 (making sure not to hit an A) would give you a tremolo on G.

Generally speaking though, you need to do a flutter tongue. But, since I can't get my tongue to move that fast, I often times default to a jazz "growl" which is more of a guttural sound. Either way, good luck!