You might be better off rewriting your background process into a simple daemon. Then you can submit the task to it and then collect it when it's done.

If the CGI gets alot of activity this model will also help reduce the load from forking. If you really felt like investing the time you could then extend that so that your compute intensive task could run on a seperate machine.

And then you could, oh, wait, any more than that and you'd be better off with an application server :-)