Or just call CO at whatever number you normally call, give them your CO PNR and they can give you the interairline ones. I've also had pretty good luck emailing onepass service center requesting the same.

I have noticed that if I do a check in at LH site, it won't let me get passes for the continuing CO flights, and sometimes I lose my seat assignemnts I made at co.com to whatever seats LH puts me in. so use sparingly. I've just used the LH code to make seat selections, and do airport checkin to keep all seating in order.

YMMV.