Ensemble Songs

Since there is no constant to whether you're in a party or not when using Ensemble songs, you can freely walk out of the AoE if you leave party. 
Also, if you Join Party -> Leave Party -> Duet casts Ensemble, you'd also receive the buff.
This allows the buff to last for about a minute without you losing the effect if you walk off the AoE. 

This might not be the nicest fix though, but for now, does the trick :P