Thanks for the detailed response with references.
I didn't realize it was limited to $5K per return rather than per person as their page isn't clear on that: Individual - Using Your Income Tax Refund to Buy Paper Savings Bonds (treasurydirect.gov)
It's also pretty silly to issue a paper bond since I'll want to convert it to electronic as soon as I get it. But bureaucracies and the people who profit from paper bonds probably fight to keep that. Oh well. At least I'll get one instead of two $5K refunds.
