It was suggested at seminar that you opt out but setup PR in case one partner unknowingly disqualifies it.

If you both opt out and indicate a PR, IRS will be confused. My guess is they will ignore the opt out election.

Odd advice - if you're doing the partnership return, presumably you'd have all the relevant information for the partners, so there wouldn't be any confusion as to whether one of them was a disqualifer or not in terms of the opt-out...but to answer your question - no, I do not think you can force the PR to appear when the opt-out box is checked.