Embed barcode in pdf file

I'm not sure this is possible, but maybe someone has a smart idea.  I've got a pdf that users are printing off our website which is used as a registration card.  What I'd like to be able to do is insert a barcode onto that pdf when it's viewed/printed, plus add that barcode to their user record.

I have a custom tag I downloaded somewhere which allows me to create barcodes in .gif or .jpg format, which has been very useful.  But...how to embed that into a pdf?  Anyone think it's possible?  I've played some with CFIMAGE for other things, but I can't see a way to use that tag to do this.

Peter