The way I have suggested before is that CCP adds several new systems or a region to high sec where there is no ganking or PVP allowed, but any ISK, ships, or modules obtained there can never leave that “safe space”, and no ISK, ships, or modules can be imported into that “safe space”. So any ISK earned there couldn’t be transferred to another player outside of it, and no ships or items could be contracted out of it. Basically negate any way for the “safe space” to affect the economy outside of it.
Or like you said, make a different type of in-game currency that can only be used in that space.