Some kind of tradecopy EA or tradecopy Script
One Master on the platform where the trades come from with one or more Slaves on other Account(s)
Hi I think its easy to use a free desk top sharing software like team viewer. you can try its free version. Download team viewer in your system and his system and then connect the PC's without even installing the software. You can view his desktop and do what ever you want in his desktop including sharing files; this is possible for 2 PC's. in this way, the licensed version allows you to connect many systems. This method will be easy for you to connect many systems as allowed in the teamviewer licensed version through which you can open the MT4 platforms in your customer PC and trade.
Another suggestion will be is instead of linking multiple MT 4 platforms, search for linking multiple PC's from distant locations which can give you more workable and cheaper results. All the best.