Best way to reduce a server's participation..

Ok, We have a two tiered system here where we have 5 boxes in front that
handle most web requests, and then a number of boxes on the back that do
only backhanded requests for certain pages.

We do also have a couple of backhanded pages that get sent between the
frontend boxes and backend boxes to try and smooth out the load when one
of them gets hammered (they are not load balanced, each one serves a
different set of users).

My question is, I'd like to see the front end machines discounted, so
that they only get hit when things get really bad on the backend. My
first thought is to just manually adjust the Arriba on these machines.
This would work for now, but if I ever wanted to balance other things
fully to these machines, I'd be out of luck.

So, is there a by???? directive that helps me with this. Maybe it needs
to be a custom module?

Thanks

-cb