DIY Reverb: Hold function?

[brand0nized]

Is there a way to mod a DIY reverb, such as the Rub-a-Dub reverb, to have a hold function like this one?

[kothoma]

The Zcat Hold Reverb is a digital pedal, most likely based on a Spin Semi FV-1 like several others of their pedals.
See also http://www.freestompboxes.org/viewtopic.php?f=1&t=14062

The hold function has nothing to do with the reverb effect per se, and you can see they also have a Hold Delay, so it's only a matter of the right firmware.
I can't see how to add anything like this around a Belton brick, for example.

But sometimes I wonder if it would be possible to create a EHX Freeze workalike with a PT2399.
Basically you would need a delay and a litte circuit to sync the input level/envelope and the feedback level/envelope.