Do you find this works with telling one payer to attack another?
I've always found this to be worthless unless you're also attacking and it's mutual. In fact wearing one player down with an alliance can be one of the most frustrating and at the same time funnest parts of the game. You need to consider how many troops you lose compared to your ally, if they are trying to manipulate you by say hitting on a 1 when you've just taken a 10, and when taking on big enemy armies, wear them down by say 10 armies each per turn. This is a necessary pitfall of no chat (not that I believe in-game chat would be a good addition)
I've had a couple where if they pretend to help while just amassing troops, you hit one of their medium sized armies as a threat which has worked on occasion and brings you both to the same understanding. For this to work you obviously need defence from them and the upper hand in at least one strategical position for the threat to be credible.
The issue with playing with beginners however is sometimes these threats are seen as something more and their happy to kamikaze revenge as they don't care about winning/losing as much as you do (more to lose at a higher rank). This obviously then puts you both at the mercy of the weaker opponent who now may be guaranteed a win.
Working out what kind of player your ally is, how much they can be trusted, and how much they can be manipulated for either personal or mutual benefit is by far one of the biggest strategical elements to the game imo.