I have just used an empty pattern for this. As long as you keep it pressed down you can have an unlimited long chain. The problem is of course that it doesn’t get saved so it’s not a real song mode but for live acts maybe thats not an issue
Actually I think you need just a first pattern switch to then be able to self-chain any pattern, so yeah one empty pattern at the start like leoparde suggest seems to be the easiest way to do it.
(not at home, so I can’t check it right know)
I forget off the top of my head where it is, I think func+scale, but you can change the length the pattern plays when it is part of a chain. Basically you can take your 64 steps and have it repeat for 128 steps. The only issue here is it will always plays the 128 steps in a chain and sometimes you only want the 64.