Option to deduct a fee after deal net and before a sales entity receives his/her split

Option to deduct a fee after deal net and before a sales entity receives his/her split

For this scenario, I have 2 agents in a deal. One is getting 80% of the deal, while the other is getting 20%. I want to enter a fee for the second agent that is getting 20% of the deal. I need an option to be able to enter a fee on that will be deducted off of the 20% of the deal alone and after that deduction would be the split calculation. 

Below would be a breakdown of a deal. The fee marked with an asterisk(*) is the one I'm talking about.

Scenario
Gross Comm: $10,000

Agent 1: 80% of the deal = $8,000
Split: 80/20
Agent Net: $6,400

Agent 2: 20% of the deal = $2,000
*Transaction Fee: $300
Net: $1,700
Agent Split: 80/20
Agent Net: $1,360