In my gliding club, there was a shorter guy who did not even manage to reach the pedals with a reasonable amount of hard cushions in the back and also was a bit too light for the forward seat of the ASK13.
The solution was to build a dedicated seat for installment in the glider. If I remember correctly, it was hooked over one of the struts holding the normal seat and then strapped down by some method. The ample space between the original and the new seat was well used to install a sufficient amount of weight so as to tackle both problems at once.
And yes, this seat was presented to and approved by the authority before being used.