1) Obama didn't really defend them on any grounds other than doing his part to placate the Republicans. (The New Yorker)
2) There is no alternative other than doing nothing and letting a patient die. (The New Yorker - science)
Why other than + gerund-participle here?
To the best of my knowledge, than, except etc are matrix licensed prepositions and the complements of these prepositions are licenced by some other elements in the matrix clause as in the sentence, I don't intend to do anything except to wait for news.
I intent to wait for news. The verb intend licensed "to wait for news".
Which element licensed "doing" after other than in the first and second sentences that I took from The New Yorker?