"I could be wrong but I don’t think this is possible. USB is a digital cable, RCA is not. "
I wouldn't worry about enhancing the break in process. Leave the cables where they are and they'll break in just fine.
If I'm not reading your post correctly and you need to break in cables this way, you should be able to do it by running the IC's through a tape loop.
Audiodharma make a suitable set of adaptors (RCA to USB) for use with their cable cooker, and while you’re at it might as welll buy the cooker as well, it is well worth the $
cost is $95