Payment Fee per vendor on Checkout

Hey!
We’re using wcfm marketplace and we have the following question.
First of all, we setted it up so that payments go directly to vendors, not passing through us.
The thing we want to do is add a payment fee for cash on delivery payment method – different for every vendor.
In our country, that service does always have an extra fee from courier companies.

We tried Smart COD but that doesn’t allow to do what we want.
We use multivendor checkout.
Is there any way to do that or any plugin that does that?

Thanks in advance!