If you're willing to work in FCP and do 8-bit renders or exports, you can try Captain's Blowout Fixer, as someone else has suggested. (Do a search and it should come up.) It indeed allows you to swap the luma information between color channels, getting rid of blown-out levels. (The luma in each channel is often quite similar.) Unfortunately, it does not render or export properly in 10-bit space.
By the way, coming out of FCP in 10-bit uncompressed 4:2:2 will only take your expanded HDV and re-format it, without discarding any information. But it is an unnecessary conversion (that could make for minor but probably insignificant round-off errors), if Color will take in HDV directly. And if it does, then it will expand it and convert it to RGB, then process it as such. Exporting out as 10-bit uncompressed might give better quality than ProRes, although often it's not possible to tell the difference between the two.
First I'd try Captain's Blowout Fixer. After all, it's free. I've used it with success to fix blow-out highlights.