an alternative is to mount them. If you perpetually water too much, maybe mounting will actually save the roots because you will be able to water to your hearts desire.
This is an oncidium I recently mounted with zip-ties, a garlic bag, some spagham moss on a stick of Mopani wood from the aquarium store. I left it outside most of 2015 and it has given me great roots (2nd picture). It is still not hanging on well enough, so I will not take the zip tie off yet.
roots close up:
I water it every day, and plan to mount a few more of my oncidiums. This is the way they cling to trees in nature, and I feel that it is the way they have the healthiest growth.
---------- Post added at 10:43 AM ---------- Previous post was at 09:01 AM ----------
I forgot to mention, it had no roots, just the old bulbs and some threads and a stump.