Fighting together

[Flashman]

I've said many times I think co-operation between allies should be limited:

I don't think the Western Allies should ever share tt with the USSR, nor Japan with G & I.  Nor am I convinced by even UK & US forces using each other's carriers.

I'm wondering what rules people have ever used for placing mixed forces under the command of a single player.

Take the example of the German-Italian force in North Africa. In some circumstances it may be an advantage for them to move and attack separately, however since room for manoeuvre on this front is limited the lack of ability to attack together could be a severe handicap.

Should players be allowed to agree to place such a mixed force under a single command, so that they move and attack together?
There would need to be some penalty, such as the pieces being handed over forfeiting a turn in order to come under command of the other player. The handover need not be permanent, and the original owner can take back control at any time, again forfeiting a turn for the pieces in question. 
Transfer would only ever apply to mixed forces in a tt, with the majority force always gaining command.

[Variable]

If you used a "General" piece for each nation, a player could choose one TT to place him in each turn to "take command" of all friendly forces in that TT. Just a thought, I haven't tried it out yet.