[racket] Redex question: parameterizing a language definition

I have a rather involved Redex question that I was originally going to
send to this list, but it got long enough that it was crying out for
hyperlinks and code formatting.  So, here it is on Stack Overflow:
http://stackoverflow.com/questions/15800167/plt-redex-parameterizing-a-language-definition

Nevertheless, I suspect that if there's anyone who can help, they're
on this list, so I'd appreciate any responses, whether here or there.
Thanks!

Lindsey