PowerShell has its own shortcut syntax for accessing the registry HKEYs, like hkcu:. It is part of the system of providers and psDrives. But other programs deal with the whole HKEY name, like hkey_current_user.
I just learned that in a registry path string "hkcu:\" is equivalent to "registry::hkey_current_user\". So if you have a long path for a registry, just tack on that "registry::", and you'll be fine. This is also necessary for any registry HKEYs that don't have abbreviations, as HKCU and HKLM do (unless you make your own PSDrive).