Improving performance for shared hosting

After using TMDA for a few years my host recently set the tmda-filter
script permissions to 0 to prevent me from running it. I noticed this
only a day later when I investigated my lack of arriving mail.

It turns out I am now receiving so many messages that the tmda-filter
script is being reported as exceeding the shared host load limitations.

I don't want to stop using TMDA, so I have considered writing a C
program in front of TMDA which provides fast, basic filtering.

However, before doing that I want to know if I can expect to increase
TMDA performance significantly, and how I should go about it.

Further, is there already a convention in place for testing tmda-filter
as a standalone run-once script? I presume it would be something that
simulates the environment variables qmail sets up for preline programs.

-- 
 kai