Just use either some electrical wire or even just some string, tie it around the master cylinder then run it through the front of the bike, down to the caliper and cut it. Then you'll be able to measure that bit of string/wire and known exactly how long you'll need and be able to ask HEL to make you custom ones.
Just make sure you run it the same route as the original hoses and factor in turning the bars from full lock to full lock etc