Originally posted by SLY
Frankly, I haven't done this , but I'm sure it should work well.

It will work, but by splitting your cable in that manner, the signal coming from the guitar will be weakened significantly.(wich is not a good thing for obvious reasons)

I strongly suggest that you get an A/B box to split the signal coming from your guitar. Something like this => http://www.whirlwindusa.com/selec.html