something like:

    void call_foo(HV* hash, SV* key)
    {
        dSP;

        PUSHMARK(SP);
        XPUSHs(hash);
        XPUSHs(key);
        PUTBACK;
        (void) call_pv("foo", G_VOID);
        SPAGAIN ;
    }
[download]

See perlcall for more details

Dave.