There is block "is_bit_forced". So you can make loop, check every bit on %M or %I-level and save comparing result to array of ebools.
As it long loop, it would be advisible divide looping to several different PLC cycles so that loop would not increase PLC cycle.
But do you really need that, when Unity online view shows Forced varriables as list at online view.
Where you need that list outside from PLC?