Actually, the mechanical process itself will be "easier" (than creating one from emptiness) but to make it "catchy" may be the tougher part :-)
For e.g., give any Bharathiyar song or kuRAL or silambu to a capable composer, they will come up with 4/5 melodies for each verse in a matter of minutes. (On occasions, this was demonstrated by music directors like MSV / IR in public even). However, whether the outcome is as catchy as what they came up purely with musical notes (and no poem) is doubtful.
I've mentioned about
this competition that used to run in our college Thamizh mag (interestingly, that too had the name 'thenRal', like the popular Thamizh mag in NA) where a poem will be published and students were asked to come up with melody for it. I had seen non-composers, engg students with absolutely no musical background, coming up with very interesting musical patterns at the hostel corridor. It should be a cake-walk for KVM-MSV-Raja-Rahman to put together a "tune" for any pre-written poem.