If you intend to replace some of the condensate return line with finned tube, it will work. Use commercial 1-inch steel pipe fin tube. Soldered copper lines will not have flexing expansion joints, so the solder joints will come loose in a while. A 25-foot length will move 1/8 of an inch from expansion. Threaded joints using 2 elbows at the dropping turns will let the baseboard move.
Afterthought (that should be thought about before installing). At the lower fittings of the expansion joints install a tee and plug instead of an elbow, so you can drain rust from the low portions of the baseboard runs (cleanouts).