If, I'm understanding your question, just install Opera using the default path. Even when you specify another install path, Opera still puts most of what it needs in main memory. I'm trusting that Opera will fix this in the final release along with the annoying default browser message.
I've decided those two annoyances are opera's way of making sure we migrate out of beta as soon as possible.
Has anyone tried all the tweaks from beta1. Do they work in beta2? I'm assuming I'll be editing my ini files this evening.