I see your question has been posted for a while without receiving a response. There are many reasons why this might be the case. One is the low acceptance rate for the number of responses received. Another possibility is that experts may feel another member of the JA community is better able to address your question.
I will do my best to help you find an answer or direct you the appropriate resources.
The issue with excessive drooling to which you refer is most likely not a new phenomena, however, due use of the bipap, it may be something you are more aware of now.
The underlying cause(s) need to be addressed. The Mayo Clinic, has a really good article on this very topic. If you are not familiar with the Mayo Clinic, it is one, if not THE, leading medical instutitions in not only the U.S. but world wide.
Basically, a medical professional needs to determine whether you have a condition called sialorrhea, which is production of excess saliva or whether an issue with swallowing is involved and address either accordingly.
At the following link click the next topic heading at the lower right to proceed. The link is: http://www.mayoclinic.com/health/excessive-saliva/MY01012
If you have not already done so, I would recommend you consult a physician that specializes in sleep disorders (e.g. from a reputable sleep clinic). If you would like me to provide you information that will help you find a physician in your area that may be able to assist you further, I'd be happy to direct you to this resource.
I hope that I have answered your question to your complete satisfaction; if I have, I would very much appreciate your "accepting" my answer; bonuses are always appreciated. If you have anything else you would like to ask prior to accepting, I would be happy to answer.
The typical options are to first try a chin strap to keep your mouth stable to help prevent drooling. If this not something wish to consider, the next option is to consider another mask, perhaps a full face mask with a built in cup. Those are the recommended options available to you.