Question concerning de captive portal idle timeout

[paketdos]

in my organisation, i use pfsense and the captive portal as a departmental firewall
so my users have have a long list of "allowed IPs" in the captive portal. and my client
have acces to network share on the other side of the firewall.

as i understand, the idle timeout is calculated with every traffic (port/addresse)
originating from the client ip.

the problem i have, is that the idle timeout never happen, because my client are accessing
some of the "allowed ip" with mounted shares or other applications

i would like to modify/hack the way the timeout is counted, by removing the acces to the
allowed ip from the calculation

i ask the question to know if someone else had tried that, and if i could get some pointer
and advice before trying

if i am correct everything about the portal is made in ipfw, is the timeout accounting
also done in ipfw.

thanks for your help or advise

PS: i use version 2.0