@Kestral: The Totem Rager's Totem Rage class ability has a similar mechanic, but explicitly allows you to allocate extra essentia to the Cobalt Rage feat whenever rage is triggered.

I could pretty easily see a DM saying no to the Incarnum Overload/Incarnum Feat trick. It seems pretty clear that it's supposed to be a 1 round boost. Were I to adjudicate it, I'd probably just add the rider language similar to what appears in Totem Rage to allow a meldshaper to reallocate essentia to the incarnum feat for one round. The next round, the character can reinvest the essentia into their soulmelds, etc by the normal swift action allocation method. It may just be me, but it seems more balanced than providing a 24 hour capacity boost.