A friendly Russia and Italy are definitely assets. If Italy moves into Tyrolia, you can count on Germany being much more wary, especially if you have an army in Burgundy.
Russia doesn't even need to do anything as drastic as move into Silesia or Prussia. Simply by taking a Northern opening into GOB and StP, they can bounce Germany out of Sweden, and England out of Norway, if he's going for the channel. Try to use this as leverage against them.
If you can't get anyone to sponsor your cause (which you should be able to, because Russia doesn't want a particularly strong Germany or England to deal with), you should play to the weaker player in the alliance. Try to coerce them, and if they are more inexperienced, a logical "seeming" argument will work, and so will merely outplaying them tactically.
If they are well co-ordinated, you might have to try more underhanded moves, such as sneaking a fleet into the Irish Sea for a free takeover of Liverpool, if England is too careless. Otherwise, your game might be near it's end. If you honestly cannot get anyone to sympathize, I would suggest...
migrating to England and holding those centres until the game ends. =D