Just found this thread, terrific. Hope the wheel and rack get sorted out. I think everyone has covered what might be possible: weight redistribution or weight reduction of equipment, epoxy glue, re tensioning spokes, etc. Another option* may be to relace the front rim to the back, and the back rim to front as the front wheel is taking less weight, but then again, not sure I'd want a front wheel to fail (would rather the rear, thanks). Since he does have disk brakes at least in a pinch he may be able to lace up a different rim or even different rim size (assuming the right spoke length.). That's tough one, here's hoping.....
*assuming he has the ability to remove the cassette and has a spoke wrench
Best of luck!