Well, I'll start off with the obvious: duct tape and/or super glue.

Have you contacted Katadyn? I can't remember the details of how that filter is constructed (and in the picture on REI's website, the connection point you talk about is, of course, in the back and invisible.)

It looks like the pump head is a different assembly - would Katadyn sell you a replacement body cylinder? Or, would they be willing to repair or exchange it?

If worse comes to worst, REI is having a 20% sale right now, which lowers the pain of replacing it from $100 to $80. (And you'd still have the filter membrane from the old filter to use as a replacement in the old one.)

Good luck.