External power supply for a DSLR flash
That works very well, but do keep in mind that some flash strobes take more than 2A from the battery pack (e.g. my 550EX peaks at about 2.7A when run directly from a bench power supply). 

Another option - which I don't know if the 430EX II supports - is to attach a HV power supply that directly charges the flash capacitor, e.g. the Canon CP-E4. This reduces cycle time and is more efficient for the batteries (i.e. you need to take less batteries with you to get the same amount of flashes).