A couple of other temporary suggestions:

If you have a warlock on another account, leave him at the boosting point. I did this and could zoom off to town when I needed to.

Recruit a freind on the main account, sign up for a trial and create a level 1, take it there and leave it there. Don't do anything else with that account (well you can use this tactic to position summoning friends all over the place). Use that friend to RAF summon the 70 when needed.

Your boosted chars can hearth and get RAF summoned by their friend, you just have to wait 1 hour to swap to the other char.

In the whole time I boosted, I only ever took my main backwards and forwards, the boostees never left the instance - over the space of 3 weeks. They were all on 0% durability in level 1 gear by the time I finished SM at 40 and it was the first time they had gone to a town.

Also when you travel, you only need to take the 70 and two characters. It's much easier to keep them alive that way. Then when you get there, you summon the other two with RAF. I did this when I moved from SM to BRD, it's a long ride through Badlands and Searing Gorge.