How to create multiple submit paths for form_for?

I've been researching this for some time and there doesn't seem to be an
easy solution.

I have a form_for that submits materials. As usual, when it edits an
existing material it automatically goes to the update action. This is fine.
However, I want to have a second submit button "Save As" that allows a user
to save another version of the material. This second button should then go
to the 'create' action.

I tried changing the form_for and added the :url => choose_action_path. Then
in the controller the choose_action_path would then use the parameters sent
through the button to decide whether to redirect_to 'create' or 'update',
but it is not working.

This must be a common need surely. Is there a good solution?

You are asking for a change to the html spec as the action is defined
in the form tag not the submit tag. That is not something that Rails
can change for you. If you want multiple submit buttons doing
different things then a common technique is to give the buttons
different name attributes (name="save", name="create") and so on.
Then, in the controller, test the name to determine which button was
pressed and take appropriate action.