Hey Gil,
The way I do it is:
1) Make up the 2 ends w/eyelets of whats hanging off the reel first.
2) Put the 2 finished eyelet end on a fixed nail on my garage floor.
3) unroll the lines down the driveway, with decent tension, and mark the pair with a permamarker where you want to finish them.You will have to walk them out from the nail to ensure they're equal before marking them. (I have painted markers on my driveway for 50', 60', ect...)
4) Roll them up starting from the eyelet end first. Your marked lines will now be on the outside of the reel so you can finish them in the shop.
I don't know of any other way to do it without the risk of kinking your lines..
There's probably some commercial measuring device like is used for wire dispensing at electrical supply houses,
but its out of my league.
Hope this helps,