[O] How to make `file+function` to accept an argument in org-capture?

[Leu Zhe]

I am starting to write an org-capture template with a `file+function` tag. It works pretty well if I put the function exactly with accordance to the documentation[1]. 

However, I am trying to make this function to accept an argument to let it find the store place programmably. 

I did some investigation on the org source, but it seems that it is not easy to work this out without hard code modification.

Can this be a new feature of org-capture? or you guys have an alternative to implement this?

[1] http://orgmode.org/manual/Template-elements.html#Template-elements