Better would be to just give a portion of the base income to the mex owner (overdrive is always shared).
Ideal would be a pop-up slider when you click on the metal resource bar. You can drag for % of base income you share, which also determines the % you get. If you slide it down to 50%, you contribute 50% less to the teams metal income pool but you get 50% less metal from the pooled income, too. You could set it to 0% to get all the income, which means opting out of communism entirely.
The problem with this is you will get passive aggressive greediness (especially with mex-fighting), but if 100% share is the default option and you only change it if your allies really arent pulling their weight (there is no incentive to do so, otherwise) it shouldnt be too bad.
Of course, overdrive is always shared.
But while we can discuss this and come up with some sort of ideal solution that fits all scenarios, it requires implementation, which is not trivial.