In 2015 I had the same question: is there no alternative for a day's roadwalk? OK, we did NOT do the roadwalk to Taynuilt; the route Jolanda and I took is this one:
From Oban, roads to Ardconnel, then take the track to Kilvaree. Before Kilvaree leave the track and try to cross the Black Lochs stream at NM 92084 31172.
This is a horrible bog to cross, but there was a metal fence in the middle of the deepest section to help us cross the stream. There is a nice ruin at the other side, Auchnacoshan, relax, from here you may pick up a track to Stonefield.
Cross the A85 and start follow a coastal route: at the end of the minor road it is possible to follow the coastline - do not go onto the railway line! When the tide is in it may be tricky to pass the rocky shore at NM 96895 34034.
Past Rubha Ban, at the outflow of a stream we spotted an otter! Here you enter an estate, Muckairn Castle, through a gate. Nice paths here, you can go right and follow one that is close to the railway line (and avoids the castle). This leads to a bridge over the Allt Nathais at NM 97734 33112 and the Muckairn Castle drive. Initially I wanted to continue following the coast, but we chose to leave the estate, walk to the A85 and follow that to Taynuilt.

Lessons learned:
1. If my partner Jolanda can do this on the first day of her first TGO Challenge, anyone can do it.
2. We saved ourselves some 11km of roadwalking, hurray!
3. If you like to wet your feet in the Scottish bogs on the first day of your challenge, this is your route.

However, I think it is wise to follow Collin's advise......

Cheers, BART

Cheers Bart, read your reply with interest, then saw your last line!!!