hippie-expand customization challenge. Possible??!!

[Sune]

Hi all!

I want to use hippie-expand for C function completion. I've but
together a script which parses my header files and lists them one by
one like so:

foo1( prm1, prm2);
goo2( prm1, prm2);

in a file I call emacs_auto_comp.

First I have updated hippie expand to only expand like below:
(setq hippie-expand-try-functions-list '(try-expand-line-all-buffers))
(setq hippie-expand-only-buffers '("emacs_auto_comp"))

This works good if I type
f<expand-key>            =>  foo1( prm1, prm2);
from the beginning of a line.

BUT if I want to expand from the middle of the row say I have already
written:

if( f

and hit my <expand-key>

I get 'No expansion found' from Emacs.

I want it to work like this:
- From current cursor position go backwards until you find either a
beginning-of-line or a space ' ' character.
- Use only what was found from the initial cursor position to whichever
of the 2 cases stopped your back tracing when performing expansion.
In the example above :
'f' was found, then space broke the back tracing
- Use the token found (in the example 'f') and expand as if 'f' was
found in the beginning of the line.
=>     if( foo1( prm1, prm2);

(I can live with the semicolon being added)

I am not Elisp-clever enough to make this happen.  Are you?

Thanks a LOT
/Sune