It's been mentioned before on this site that the 'whiteboards' are laminated pieces of white paper and markers will be given for writing on them. No working is to be erased from these boards, though you can erase to re-write if you make a mistake (quite dumb, if you ask me). However, it seems that this format will be here to stay unless Pearson decides on something else.
Since this thread is about strategy, I'll try to suggest something which you can try out.
I've never seen the whiteboards before nor taken the Pearson administered GMAT, so I can't comment on the quality of their boards (smooth/rough, reflective or dull etc) or their markers (fine/medium/thick, smudge etc). However, I suppose you can try and laminate your own piece of A4 paper and practice using a marker, as opposed to using pen and pencil. Yes, it's a hassle, but I supose it's better than adapting on test-day itself.