Double up a li-ion battery pack?
The answer, sadly, is 'it depends'.

Adding a parallel set of cells will at least halve the impedance the charger sees. It probably would be able to handle it, but you should expect longer charge times and/or higher temperatures. And on the first couple runs, I would be ready with a IR thermometer and a fire extinguisher, but I'm kinda paranoid.

Note that you said "identical but higher capacity," which isn't really possible. Higher capacity cells in the same size typically have lower internal resistance, and that can also change the dynamics of the situation.  It shouldn't be a problem, but it's something that should be noted.