Hi pianorob
Here is what I do.
I trill in measured demi-semiquavers. I start the trill on A, so I am trilling downwards. Every time there is a higher melody note, I make this the first of each group, so that the A is missing. The aural effect of this is fine, even though not strictly 'correct'. It has the double advantage of freeing tension that would otherwise build up through having to emphasise a high melody note at the same time as playing a trill note. It also makes it easier to bring out the melody. The rh G that is both melody and trill is difficult to bring out; sometimes it works, sometimes not.
I finish the trill with a triplet of demis G-F#-G on the final LH semiquaver.
My trill is not always as even as I would like, so I use loads of pedal - partly to cover this and partly because I like the effect. The first time I tried pedalling this passage, I was amazed to find that it stands a pedal change on each crotchet beat. The lh rush up the scale of C sounds particularly impressive; I did not expect that.
No doubt the likes of Ashkenazy, Lang Lang, Axe et al can play a more independant trill; I am not in their league and have to settle for less. I have recorded my solution and it sounds impressive.
Hope this helps
Steve