I've been thinking that too Dave. What about the sump plug though? The oil comes out horizontally the split second the plug leaves the thread, then the angle gradually reduces until it's vertical. The hole in the undertray would need to be big enough to accommodate the change.
The solution is one of
these. Then it's just a case of: 1) remove undertray hole cover. 2) Stick your hand in and remove safety cap from drain valve. 3) Attach drain tube to valve - oil starts to flow down tube into your container. 4) Unscrew oil filter. 5) Go and have a cuppa while engine drains down.
See the video here-
https://www.youtube.com/watch?v=L0T3FUQJB_w - his is slightly easier because the sump plug faces vertically downwards.
The hole in the undertray now only needs to be the diameter of the filter (call it 80mm) plus the width of your hand (say 100mm) = 180mm. I reckon a 180x100mm hole in the undertray would be big enough to get to the filter and the drain valve. All it needs then is a cover plate for the hole (plastic or aluminium sheet.) and some fixings.