You can make "drafts".  Ebay says you can only do 20 at a time, but thats not exactly correct - it holds an indefinite amount, you can only see the last 20 youve done. As you list them, the others will come forward.

Just make a new listing and hit "save for later". rather than continue. Ive made up to 80 at a time, then panicked when I could only see 20 lol. the others were still there, just hidden.

I do this alllll the time - when I feel list listing stuff I make a whole bunch of drafts and list them later when freebies are available.