Not trying to bring the rain to the parade...
But your initial idea of just blowing through a filled 4" pipe would be alot better, im assuming your probably running a 120mm fan for your exhaust as their most common, but they match up to a 4" ID pipe quite nice.
You're gonna find that this last one is gonna restrict the airflow Alot, apart from the carbon slowing air down anyways it pretty much needs to be mesh on the inside and outside to allow air to flow the easiest it can as really it's just there to hold the carbon in and also the inside should be the same diameter as your exhaust for it to be more effective.
Only other thing i guess is pantyhose works and is cheap, so continue using it if you desire, but if you can run a bigger mesh that just holds in your pellets that would be even better still.
Also once you have a filter hooked up your fan will sound quieter as it will be muffled.
You get it all reasonably dialed in time.