Also note, if you do ANYthing else that requires a standard or partial action -- even if it's an EXTRA partial action form haste! -- you lose concentration.
Sounds to me like you may want to pick up the spell "Sonorous Hum" (from Savage Species; Sor/Wiz 2; [sonic]; 1 minute/level duration, the very next (concentration) spell you cast, the Sonorous Hum takes over for you, leaving you free to cast other spells ...).