I can think of no place where Tolkien does anything to explain the trolls' names. If he had ever done anything, I would expect that he would have done the same as he did with Sam, i.e. find some other name that could be shortened into Tom (Samwise instead of Samuel — surely something could be invented for Tom as well).
Story-externally, I think this is another example showing how Tolkien was working with The Hobbit. It is clear from the early drafts that The Hobbit wasn't so much eventually drawn into his Silmarillion world (as he seems to imply in later letters) as it was allowed to borrow from that world from the outset, but, and this is the important bit, without ever being intended to be a part of that world. Tolkien liberally borrowed from his mythology to provide a background for his children's story, but he never meant the story to actually be a part of his mythology. Because of this, Tolkien felt free to introduce elements into The Hobbit that he would never have accepted into his mythology: the ludicrous talking purse is another example. Of course, once the sequel became firmly rooted in, and a part of, the mythology, he suddenly had a story with several components that were incongruous with the overall atmosphere of the mythology, but which he was forced to accept. His work on the 1960 Hobbit — even though it never reaches further than the start of the third chapter — shows that he did accept these elements as he didn't make any attempt at deleting them (the names of the trolls are unchanged, and even the purse is retained).
Troels Forchhammer, physicist, Denmark
The love of Faery is the love of love: a relationship toward all things, animate and inanimate, which includes love and respect ...