It's a tricky situation.
Are they firing Sparrows at the full 55nm?
If they are, I'd try to get them to commit to an engagement on some of my aircraft at extreme range, and then turn and run with those. If you time it right you may actually be able to outrun their missiles, or get low enough that their missiles lose range and run out of fuel in the dense atmosphere (caution: not always very effective against a lofting missile). Additionally, if you're low you put yourself in the most agile position while the enemy missile is suffering range penalties. While the Sparrows are guiding in on your first planes, the other F-18s can try and make a high altitude burner dash into range and make their own engagements.
If they're holding fire to wait for better hit chances at closer range, then you may be able to get an AMRAAM into the air at about the same time they launch their Sparrows. If you've both shot at about the same time, immediately cut throttles and crank, to reduce your rate of closure. If they're auto-evading, then you will have the advantage, as a single missile inbound will often make them flinch as they turn to beam the incoming missile. Try and steer so that when they turn away from your missile, you are heading outside their illumination arc. If that works then their missile loses lock and goes ballistic, while your active radar missile is still inbound and effective.
Depending on the terrain, you might also look at opportunities to approach under cover of an escarpment or mountain range.
If you have noise jammers (OECM) that might give you a few extra miles of free approach, but you have to be right on the line between the jammer and the illuminator. The jammer doesn't have to be in an airplane. Sometimes you can pull this off with a jammer on a ship.