We went from the youth hostel (http://www.streetmap.co.uk/map.srf?X=207910&Y=820295&A=Y&Z=120&ax=207940&ay=820220) along the obvious path. That took a good few hours and was only about 50% ridable.
You could push up the ascent. It'd take ages, but it's mainly hard pack. You could probably MTFU and ride most of it. You'd loose the epic wildiness feeling tho you get from going at it the long way round.
We started here (mountain rescue post carpark):
http://www.streetmap.co.uk/map.srf?x=196095&y=821095&z=120&sv=196095,821095&st=4&ar=y&mapp=map.srf&searchp=ids.srf&dn=671&ax=196095&ay=821095&lm=0
We went along this double track (all rideable):
http://www.streetmap.co.uk/map.srf?x=199120&y=818320&z=120&sv=199120,818320&st=4&ar=y&mapp=map.srf&searchp=ids.srf&dn=671&ax=199120&ay=818320&lm=0
Went via this path to the youth hostel, about 50-70% ridable I'd say. We generally strap it on and MTFU but some of the climbs required sticking bike on back:
http://www.streetmap.co.uk/map.srf?x=201275&y=817260&z=120&sv=201275,817260&st=4&ar=y&mapp=map.srf&searchp=ids.srf&dn=671&ax=201275&ay=817260&lm=0
The bit after here is all rideable to the YH.
http://www.streetmap.co.uk/map.srf?X=204185&Y=817305&A=Y&Z=120
If you wanted to make a (even cheaper) night of it than using the youth hostel, there is a brothy here (http://www.streetmap.co.uk/map.srf?X=205310&Y=818415&A=Y&Z=120). It may or may not have a roof at the moment (I seem to recall something about not burning some railway sleepers that were being used to hold some roof supports). Bare in mind that there is litterally nothing to burn in the vicinity unless you catch a particuarly dry deer.
Timing wise (from camera exif data) we left the car park at 13:30. Got to the end of the double track at 14:10 with photo stops. Top of the climb at 15:20, got to the YH at 17:00 with a fairly major crash. Not sure what time we left the next day, but it wasn't particularly early. Got to the top of the singletrack at 10:50. Finished the ride at about 11:50 (including photo stops and punctures).
PS. If you do ride it, MTFU and jump in the river. It's er, refreshing.