Yep, I ended up using my wife's account. I have one tiny unresolved issue. Our 2nd Sony came with a sticker code for "$10 off a single e-book" credit.
I have been unable to claim this because the first reader, and therefore our account, is registered to a non-Borders-bought reader and the code is not accepted. Customer service has NOT resolved the situation to my satisfaction but I'm probably going to just blow off the $10 loss rather than attempt an end-run involving a second PC and new Borders account.
I'll just hold an unreasonable grudge against Borders and go out of my way to spend an adsurd sum of money on e-books elsewhere.