Adding a quarter note under an existing triple note?

So I'm trying to add a quarter note (G) under the existing triple note - meant to be pressed by the Right Hand Thumb - as in the picture, but how can that be done without affecting the triplet notes above?

I feel I have this kind of problem all the time with any other note combination where a longer note should extend to cover the time a a few shorter notes, so I wonder of there's any other way than to repeat the note connecting them with a with a slur for a "longer" duration?

//Rolf