Currently, PrepareParallel launches local kernels only. It's relatively easy to setup remote kernels under "Preferences->Parallel->Remote Kernels", however they would not be started with simply LaunchKernels[number]. For demonstration, I added a simple option Parallel->AllConfigured to PrepareParallel that will launch all configured kernels, both local and remote:
MatchQ[parallel, AllConfigured],Here, I don't try to do any kernel bookkeeping, so I just close the current ones and launch all configured ones as new. Ideally, one could imagine some fancy bookkeeping where for a certain number of requested kernels, first local kernels are started, then remote kernels and at the end additional local kernels.