How to prevent appdomain unloading in w3wp.exe

[ibenc]

Is there a way to prevent w3wp.exe from unloading a particular
appDomain. Some parameters, config files?

Here is some info about why I need this.
I have a long running background thread in asp.Net application.
Occasionaly, especially during peek CPU usage, the appDomain of
the application gets unloaded by the w3wp.exe, and the background
thread is terminated (we receive thread was being aborted exception).

I guess the reason for unloading appDomain is that the domain is
not getting any requests, since all the processing in the domain
is being done by the background thread.
I know this is bad design, but some quick fix solution that would
prevent appDomain from being unloaded would help

tnx,
ibenc