Hi !
You can use any of the three Random sources for that.
Sample & hold with White noise as source and "Poly KBD" for Trigger would be the obvious choice if you want purely random values, but you can also use the two other modes:
-Binary (if you want to alternate between two specific values)
-Turing (if you want a random that is a little bit more "musical" and sequenced)
As well as the LFOs like you mentioned. In that case, set their rate mode to hz and the rate to the minimum. That should be very slow, slow enough to prevent it from changing value before the next key press.
Best !