Undo fast-forward merge without using hard reset

Question

I'm using git with Sourcetree. I've accidentally fast-forward merge and pushed to remote. Now I want to undo this. I know there is a way like this:

1. hard reset to commit before merge
2. force push to remote
3. remerge

But, i know that hard reset is dangerous. Is there any other way to do this? with steps included.

Thanks