First, thank you for working on this. Perl-On-A-Stick will be very handy. It's a great idea. Good luck!

Does the U3 command prompt require a U3 flash drive?

Would it be possible to use the PortableApps.com command prompt instead?

I haven't used either PA.com or U3, so I am not sure about the relative merits, other than PA.com is open source, while U3 is proprietary. I've been meaning to investigate this stuff further, but I've been rather busy on other projects. Sadly, it seems all my tuits are square these days. In any case, you may wish to consider PA.com, unless you already have and chose U3 due to it's technical brilliace, or beautiful logo or whatever. For all I know, it may even be trivial to accomodate either command prompt.

Anyhow, thanks for pursuing this and good luck getting it working.