Yes, this is possible. HotSawz does not have a freeze function, unless I am misunderstanding what you are asking. Polyphony and PolyFlex both have freeze performance parameters, which allow you to play a note/chord and freeze it using one of the footswitches.
Insert routing isn’t needed for this. If you route the H90’s presets in parallel, you now have 1 path for your freeze, and the other path for another effect to play along with the freeze. Turn Kill Dry on for Polyphony so there is no dry signal that passes through.