I wonder if their might be an out of the box way to 'lock' or otherwise control structural member length to even two inch? (1'-0", 1'-2", 1'-4" ...)
This would be for strut. Strut has slotted holes on two inch centers. It is common to always cut between the holes.
If there is not such a method... I wonder what other idea that might be easily implemented?
I'm not aware of any way to force the structural member to a 2" increment but you can always specifiy an exact length during placement, adjust the length using the property palette after placement or set the SNAP increment to 2" during placement to make it easier to draw at 2" increments.
I hope that one of the above suggestions helps.