From a priest…
While I mourn the resignation of Pope Benedict I also mourn the fact that there is no particular Mass text with which I can pray for his health. If there were to be a Mass for a retired pope, what might that look like?
I’ll confine myself to the older, traditional Roman Rite.
I think you could during a Votive Mass simply add the orations Pro Papa. I say this because they are virtually identical with the prayers Pro Episcopo, with the exception that in the latter you also name the bishop’s church. Benedict remains a bishop, after all, and his church was The Church. Also, were you to say Mass for him on the anniversary of his episcopal consecration (28 May), you could use – mutatis mutandis – the Mass In anniversario Episcopi.
Perhaps others have solutions.