Exactly. Zip tie trick works the best. Make it the shape it will be on the sled. There is a video on Burandts site by Volk that shows this. Then it’s a 2 second job.
So the little 3/4" spacer behind your secondary retaining bolt happens to fit perfectly in the top gear. So use the bolt without a washer and install the spacer on the top shaft. Slip the belt on half way down on both gears. Start the lower drive gear on the shaft, then pull the top gear over the spacer that was installed in the top shaft. Acts just like how the tool is supposed to. Then hold the brake lever, and spin the track a bit to line up the splines. Works best if the belt is warm. I found that the tools would rattle around my bag, and beat up the threads... Making them useless.
Zip tie is a charm ...
Before you remove the pulleys & belt take a picture or mark where the belt stops touching each of the pulley on both sides.
When installing zip tie bet onto pulleys in same location as noted and then enter both pulleys onto splines at the same time working both on at the same time or each just a couple of mm at a time so one doesnt bind. Once bith pulleys are well entered on splines you can use a little persuasion to help to finish them off.