You most certainly can, using the same procedure to transfer fluid from the No2 to the No4 system.
The reason for the transfer is the reserve brake shuttle valves. Also the restricters in the alternate brake source selector valves.
Selecting No. 4 (B747) or Right system (other Boeings) keeps the shuttle valves in place.
Only a very small amount of fluid "transfers," and to do anything meaningful, one would need to switch systems repeatedly. Starting another hydraulic source prior to #4 doesn't create a continuous flow of fluid. System 3 has no effect, and system 1 will only work if the normal brake selector valve is selected to secondary system 1. It doesn't automatically pressurize the brakes unless selected.
What am I missing here?