I might be misunderstanding what you need, but perhaps a hopper clock modified to fire once could do what you want.
It's the same as a regular hopper timer, just replace one of the sticky pistons with a regular piston. Then, after the cycle completes, the redstone block will be left on the retracted sticky piston, which should be activated. Then you can trigger the clock to cycle once when you update the sticky piston.
If it works, I should have a screenshot of it built.