The obvious answer is to practice and study in the game that is your weakness. You've noted that you're already doing that, which is certainly a good step.
That said, you will always have some games that are more of a strength than others. My solution is, quite simply, to play extremely tight in the game(s) that you are weak in. By only playing strong starting hands, you will face fewer tough spots in your weak games. Then you can use the games that you are good at to "play poker" (i.e. exploit weaknesses in your opponents, make plays, etc) and amass chips.
The only place this falls apart is if you end up playing in your weak game while holding a short stack. There, your stack is going to do so much to dictate your play that you will have to take some chances when situations call for it. This, however, should be an area that you're reasonably well-equipped to handle, since you have a good background in related games. That is, because of your related knowledge of other stud games, you should be able to spot typical stud stealing spots, and have enough starting hand knowledge to know what's good enough when you have to make a desparate move.