Block all HTTP connections except Fiddler

[Luke]

I am trying to use Fiddler to debug an application, however I would
like to ensure that all traffic is going through Fiddler. Is it
possible to setup Fiddler so that any traffic is blocked if it doesn't
go through Fiddler?

I have tried setting up a Block all outgoing HTTP requests on port 80
in the Windows Firewall with Advanced Security. That rule blocks all
the HTTP traffic on my computer (i.e. I can't go anywhere in IE or
Firefox and Fiddler can't connect). However when I also specify a
rule to allow the Fiddler.exe application it is still not permitting
Fiddler HTTP traffic.

Any ideas how I can do this?

[EricLaw]

If you use Firewall rules to block all applications other than Fiddler
from using the network, then you should get the effect you want.