My PWD will not sign a LPA am I as his spouse legally entitled to make decisions concerning his health and welfare.
I am not concerned about the financial aspect as he has no assets
I think the short answer to this is 'no'. However, medics may listen to what you say(that may not always be the case though), even if they don't discuss the matter or act upon what you have said.
Without an LPA deputyship is required once the person has lost capacity and that can be expensive.
Health and welfare deputyships are extremely rare, the COP preferring to deal with each decision by means of a separate court application at ~£400 a go plus cost of formal proof of incapacity.