FastLane does allow motorcycles, or at least they used to. I originally got the speed pass for my car. I stopped by the fastlane dept and was going to get one for the bike when I found out I could simply add several vehicles to the same speedpass acct. They don't care who uses the pass as long as it goes off on entry and exit. The problems arise when it doesn't go off. Which can happen on occasion with the bike. If it doesn't go off and they don't find your plate in their system..
Except a $50 fine.. hehe If you add your bike to the acct and the light doesn't go off.. they charge your acct some amt ranging between $2 and $3.30.
If you currently have a speedpass and want to use your bike in the fastlane you can simply goto their website and add your vehicle information. As far as getting a new one I think they'll allow you to get one for a motorcycle still but I'm not 100% sure on that.
-Feir