rebase?

upstream:

A -- B -- C | develop

I fork upstream and make a new branch (patch)
   P1       | patch
 /
C           | develop

I then submit a pull request.
Since upstream won't merge my PR quickly, I merge my patch branch on the local develop branch to start using my work.
   P1       | patch
 /    \
C  -- P2    | develop

Then upstream does some changes to develop:

A -- B -- C -- D -- E

I do "git fetch upstream", now I have:
             P1       | patch
           /    \
A -- B -- C  -- P2    | develop
           \
            D -- E    | upstream/develop

And I want:
                       P1     | patch
                     /    \
A -- B -- C -- D -- E  -- P2  | develop