I run through act 2 with say a summon necro to plough the road. Get all the staff parts, cube, kill the summoner, kill duriel and go to act 3.

If i rejoin with another character now, the problem i have is that i can't get into the palace. If i could, i imagine that i can run through the arcanse sanctuary, take the portal, go into duriel's tomb, talk to tyrael, get the quest done and move to act 3. It would save a lot of time searching for the parts.

Is there any way to circumvent this problem?

Solo - no.

Multi - really fast way - it requires another player, but you just have to be in Act2 when the other player talks to Tyrael after killing Duriel - it will complete your quest and allow to speak to Jerhyn -> Meshif -> sail east. Of course you have to talk to Jerhyn which might be in a palace, but he should be reachable after few tries.

I see. Yes i know how it works in multiplayer..