I verified that it works in both the 430 and 430W trainer. I can't imagine
the 530 trainer(s) would be programmed with different logic than the 430's.
As a shortcut, you can insert the user waypoint name (as long as it is
unique--in my example it was "PD270") in the desired spot in your flight
plan and the unit will prompt you whether or not you would like to create a
user waypoint. After pressing YES, it will take you to the user waypoint
creation page.

Once you hit ENT, the unit will fill in the distance value automatically
since it already has two datapoints.

Hope this helps.

Marco