Eventide Staff
There is currently no freeze/sustainer Eventide algorithm, but I have mentioned your request for one to the developers.
You could try some of the H9 delay algorithms (9101-9109) that include the "repeat" on/off switch in the "config" settings. If you set a short delay time and engage the switch while a note is playing you can get a similar infinite sustained sound, but with varying results. You might like this option as an alternative to the reverb freeze sound.