I guess, you are right. The only way to connect an external GPS receiver is via Bluetooth. Which make the whole idea very expensive and impractical.
By the way, Toshiba Thrive tablet which I own, has a full size USB port. But it does not help much. As far as I understand, in Android world there is no drivers as such, it must be an app, which handles an external device. I could be mistaken though.
Thanks for the prompt reply.