Well, Asp beat me to posting, and he has more developed ideas than I. Here's what I was posting anyways:
Haha, I've long been meaning to post exactly this. My two main warbands are lizardmen and skaven, and I really, really want to use blowpipes for the same reasons as you, but it's an exorbitantly expensive item which is far inferior to a sling or showbow.
At a minimum, give it 16" range, or 12" range with no long distance penalty, and increase the strength to 3.
I wouldn't give this to one of my four skaven heroes capable of wielding it, or even to one of my lizardmen heroes, but I'd toss one on a skink henchman for fun if I had lots of extra gold (it'd more than double the model's cost in gold).
Allow the above upgraded weapon to be used with quickshot, and I might run one on a hero. I'd still prefer a QS crossbow or knife fighter thrown weapons nine times out of ten though.
As the warhammer blowpipe is range 12", S3, with 2xMulti Shot, you could houserule something along those lines as well.