Is your main aim to get the mortgage or get the mortgage protection? If it just to get the mortgage then check with your bank if they will accept a waiver of mortgage protection on him as they are allowed to do in a case like this although not all operate this policy.
If you really want to have the mortgage protection in place too then I think there is some specialist company that may be able to get you a quote, don't know the name but saw it mentioned here before so someone will probably be along with that info.
It's not a given that he will be able to get cover at any cost, companies have their own underwriting rules and if they refuse there is nothing much you can do other than go ahead without the cover if the bank is agreeable to the waiver.
Does he have any life cover through work that would at least be there should anything happen? The bank won't accept this but it would a bit of security from your point of view for the mortgage.