Sometimes bass parts can be played on other instruments too.. maybe Mark can handle it in the guitar parts.. I know a friend of mine's band lost their bassist a couple years ago and now he (sean/friend) plays the basslines on the keyboard/organ.. and their guitarist, James, covers some lines in the guitar as well. FYI, they are called Square and have relocated to LA (they used to be in Lincoln, NE and called Happy Dog until they won the Ernie Ball Battle of the bands a couple years back and got a record deal.. check out http://www.squaresounds.com if you are interested.. their music is definitely, uh. interesting :)