Question on Time Control

This may come out to be an odd-ball question but here goes. 

Is there a chess clock out there in which I can set up a time control of let's say G/25, however, the player only get's the bonus time of let's say 30 seconds if they spend >30 seconds thinking on the move.  If time spent is less than 30 seconds/move you don't get 30 sec bonus.  

Cheers,

Leo

Kind of. A clock that supports Bronstein delay does something similar but not exactly.

With a 30 second Bronstein delay, they clock will start automatically and when the player makes their move, they will get the time used back, up to 30 seconds. If they use 20 seconds, only 20 seconds gets added, if they use 35, 30 gets added.

Yeah, I kind of knew about the Bronstein delay but is there a way to hack it to do what I want to do.  Essentially, I am thinking of some motivating ways for my son to do thinking than making a move instantly.  Thinking --> more time available, instant move --> less time available

I'm not aware of a clock that has an option like that.