I've been in this situation before.

One thing that has helped me on occasion has been to remove the
carriage assembly completely, then run the machine through a couple of
load/eject cycles (if possible), watching the driving gear(s) to see
how they moved during eject and load. Sometimes this is easy to do,
sometimes it involves bypassing some detection switches or fooling
light sensors, sometimes the electronic interlocking used is too
complex to be fooled into thinking the carriage assembly is there when
it really isn't. Might be worth a little investigation, though.
Cheers.