Thanks Polly
Not sure about alternative routes on this one. Its quite an awkward one to get at. You could go up the way I came down. Stay on the track to Connonish Farm, go over the wee bridge there then go straight up onto the ridge. Its steep and there's little or no path most of the way. It would be a tough old climb up. Other than that you could maybe get to Oss the way that I bailed out after doing Lui, via the Allt Coirie Laoigh up to Creag Dhubh a' Bhealaich. This might be a bit easier on the legs than the steep slope at Connonish farm but again there's little or no path.
The forest is a lovely place to walk through, especially at this time of year. Its just very boggy which makes it hard going sometimes. Really wouldn't want to have to come down through there after a long days walk with tired legs. That's why I got out the other way. Good luck with getting Oss whichever way you choose to get to it