A quick search shows HK had a harness (
http://www.youtube.com/watch?v=l4t7-Y3u-04) but complaints that it didn't work right. But I don't see it available on the website.
It should have only 8 wires in the final plug - some comments said it shouldn't. Because two wires on your 3s and 4s plugs are attached to the same spot in the battery stack - you don't need both in a 7s config. You could make your own adapter harness or replace the two taps with a single one (carefully) - or charge through the balance taps (is this what they expect people to do?)