This is a similar technique, but doesn’t require anything other than a bit of masking tape and an Allen wrench.
Step 1
Create a loop with some masking tape (higher-visibility, like blue or green will make this a little easier later). Embed the belt in the makerslide track:
Step 2
Roll the carriage over the belt and loop until the top of taped portion is directly under the pulley for the x-axis. This should leave the loop you made between one of the idle wheels and the pulley if you’re looking directly down on it through the carriage:
Step 3
With an allen wrench, reach down and hook into the loop. Pull the loop up through the carriage until the entire taped portion is above the carriage, remove the tape, and loop it over the pulley.
Step 4
Tension the belt as was done for the Y-axis belts.
Good luck, and I hope this helps some folks!