I'd just put in a shutoff valve and a tee between the tank and the new valve on the line going to the pump. On the Tee, I'd add on about 10" of tygon tube and use a dot/plug to cap it off. Make that tygon long enough to keep your oiling connection outside of the plane. That way, any oiling spillage is outside the plane. If you want to get fancy, one could use a fuel dot in the fuse and just pull out the oiling line out to fill the tank w/o removing the cockpit/canopy. If one wants to stay scale, install an access door/panel along a panel line and hide the whole thing behind the door. Just a matter of how much work you want to put into it and how scale you want it to be.