merging unmanaged working tree

Hello.

Is there a method to (dry?) run git-merge to detect conflicts
on:

* current HEAD (or working tree)
* selected previous revision (the one used to "branch")
* directory tree (or a single file) "branched" with git-archive

I'd like to synchronize portable working tree but don't want to keep
history in it.

-- 
Miłego dnia,
Łukasz Stelmach