Attaching to a running CMUCL process

Other than using detachtty/attachtty, is there any way to attach to a
running CMUCL process and have access to its top level?

I tried using gdb with the process id, but the stack frames and symbol
tables I got back were meaningless (they all said "??").

I thought I could start a new CMUCL process, and attach to the other
process using its pid, but I couldn't find anything in manual which
indicates how to do that.

Is it even possible?

Unfortunately, I can't run the process I want to monitor under detachtty.