In respect of EU citizens...
Not if there are bonuses to their based on playing/scoring/clean sheets/etc. This would be considered discrimination. You cannot restrict someone's ability to be paid an employment related bonus based on their nationality!
You would have to remove ALL incentives...
How?
The only way it can happen (realistically) is for us to withdraw from the EU!
We just do not have the negotiating power for convince the EU to offer an exclusion for the English FA to avoid the consequences of the EU Directive on free movement of labour.