You need more than a splitter, you need to isolate the ground or remove its effects. Take a look at these.
A few pre-built items:
$59
http://www.audioxpress.com/bksprods/...t/pj-vr1ff.htm
$99
http://www.audioadvisor.com/store/pr...p%20Eliminator
$99
http://www.audioadvisor.com/store/pr...0TV%20Isolator
$149 with splitter!
http://www.audioadvisor.com/store/pr...ble%20Splitter
I would bet you could find a schematic for one, but that would only be recommended if you are good with a solder iron!