Yes this is doable, but I could not get past the stupid "Moor Prowler" who nailed me every time on the way into the valley just before the Rivendell entrance. The 'Paranoia' feature doesn't even reveal him when he's hidden, and he's in a different spot every time I regain the patience to spend an hour getting there again. This has got to be the worst part of the quest available. If you want to do this quest with out having your last hour go to waste because 'Paranoia' can't detect hidden creatures like it is supposed to, bring a friend to aggro/clear the way ahead of you. Please don't keep trying and get frustrated like I did, just get a friend to go along with you. Good luck!
It is definately possible to do solo. The quest gives you 2 and 1/2 hours. It took me 30 minutes to get to the last bridge. I stayed on the road the whole way until just past the Ford of Bruinen. Once you cross the Ford and start up the pass, when it reached the first switch back to the left, head off to the right instead. Continue to climb to the top and then head to the Gates of Imalris. I stayed in 3rd person view, with the camera backed out as far as it would go and I used the Left Mouse Button to look around so I could see what was ahead of me. I took me about 25 minutes to get across the Trollshaws and I completed the quest in just under an hour start to finish. The key is to be patient and go slow, plenty of time for the quest.