Glue it in. I'd use JB Weld and make sure it all stays outside! Just measure the correct amount of oil.
There are a couple of Simms pump hacks you might be interested in? Remove the overflow vent hose and plug it, then drill a small vent hole in the filler cap. This stops all the overflow getting in your tray or stops having to waste time with a catch bottle. You might find that the filler is already drilled, if you are lucky. The other one is to remove the drain plug and machine a small adapter to take a small brass tap. Then you can stop opening and closing the plug and running the high risk of stripping it.
You do religiously change the oil every 50 hours? A ziplock bag is the best way to catch the oil.