i had a 10" splash stacked over my 18" crash/ride (which i mostly use for crashing) but didn't use it for very long, it got in the way and i didn't use it very much. the other thing you should consider is an arm that clamps to the cymbal stand under one of your current cymbals. a friend of mine had an 8" splash inbetween his crash and hi tom, and it worked really well. if i was to ever mount my splash back up this is where i would put it.
*edit* looks exactly like this