Make evasion an in game item. They have rings of evasion in PnP for 25,000gp. Add it to a raid item list, make it a Tier 3 upgrade requiring Comms plus other stuff or make it a quest chain end reward option. Make it a Blue augment ML 28 that drops only in certain locations (personal choice).
Second solution - capstone for Fighters granting evasion for 1-2 minutes/clickie. This can be used in conjunction with the fighter attack/haste type effects from the enhancement tree. Even adding evasion as a capstone still will not win over a lot of the martial players from taking monk levels, but it is a start. Until Turbine reassesses how multiclassing works and adds some penalty for doing so people will still continue to multiclass.
Third solution - level 28 martial feat requiring two destinies within that martial sphere to be capped before you can take it.