I don't know. 400 mg, tightly packed leaves about 1/16 inch remaining in a 00 cap. No room for the 90 mg ledipasvir-so I make 1 sof, 1 led. I think you could get 490 mg in two 0 sized caps.
You can make it work.
The Profunnel works great, but you can just fill the large, bottom portion. I imagine, from my experiece, you could tighly pack 420-430 mg of sofosbuvir in it. When you snap the smaller top portion on, there will be some space. So its not completely full. I don't think the funnel is made to work any other way, but I don't know that for certain.
My first patient on generic APIs is now past SVR12. His method was simple - weigh on a teaspoon, swallow with water. Capsules are a convenience mechanism, as are tablets. Don't over think it.
If you want to use filler for volume based filling of multiple capsules simultaneously use lactose from the baby section of the chemist and grind the API and lactose together in a mortar and pestle to equalise particle size and ensure a uniform mix.