You'll still have to audition. Regardless, get yourself an inexpensive interface to record into the computer and if the software doesn't come with something similar to it, get garage band so you can create some actual songs with you playing bass to them. This will go further than just playing bass to a 12-bar blues or a slapfest that may turn people off from calling you. Put a variety of stuff there too - one pop song, a jazz song, funk, etc... check out my own myspace for some examples if you'd like -
www.myspace.com/bassjones - also, make sure you set up an artist site, not a personal site as they won't let you convert them now - or if they do it takes forever!