In short, not easily if you don't have the equipment to count chromosomes, I think. Tetraploids are supposed to be bigger plants (noticeably the stomata), but as for triploid, nobody's mentioned any discernable differences between a diploid and triploid, so I'm not sure there is any way to tell short of counting the chromosomes.
I asked the same question a few months back and there was a bit of a discussion on it here, just in case you hadn't seen it:
The thread "Ploidy" in
Lilies forum
