Using a Wireless Card for internet on my iMac & sharing it through Time Capsule?

So, I moved to a new place, where there isn't any great options for internet... but there will be in a month or two, so I'm temporarily using Cricket Wireless, which is a USB connected wireless modem (much like the ones AT&T, etc. sell). It works just great on my iMac, but I'd love to be able to transmit that connection through the Time Capsule, so that my Macbook can pick it up, too.

I know how to set up Time Capsule the "regular" way, of course, but I can't do that with this USB wireless card, which requires it to be run through a PC or Mac, so that you can install their software, etc.

Anyone have any ideas for how I could do this? I had it working on a PC prior to this, just by enabling internet sharing for that Cricket wireless connection & hooking up a router to my computer's ethernet port. Is there an equivalent procedure for the Time Capsule & iMac?

Thanks so much in advance for any help!