I know that I can play a b2 Dorian scale over a DomSus chord with a lowered ninth, but what about over a major7 b2?
You probably won't encounter this chord very often, but you could derive a synthetic scale for it. A synthetic scale is made by altering a traditional scale to fit your purposes.
In this case, you could play a major b2 scale. For Cmaj7b2:
C Db E F G A B C