I tried the sound, and it's certainly doable.

I thought I'd knock up a possible symbol in paint - it's an amalgam of the
symbol for the voiced bilabial fricative and the belt from they symbol for
the voiceless alveolar fricative. You didn't say if your sound is voiced or
unvoiced. Anyway, I've put the symbol on the web at:

I hope you like it.

I've been doing a bit of symbol designing actually, I did an alternative
English alphabet. Probably not the right place to show it, but what the

Maybe you can use some of the symbols or adapt them.