If Wwalrus is still listening, learn to play the piece two ways. One way is for performance on an upright, and involves making changes in the score to make a suitable sound.
The other way is using the sostenuto pedal, which is a nice feature, but is generally not available in any performance venue that would allow me to play (church fellowship halls, nursing homes).
For example, on some fifteenth span chords in Pictures at an Exhibition I play some bass notes in the middle of the right hand chord on an upright. On other fifteenths with non-simutaneous stike time, I play the bass note with the heel of my left foot (with socks and no shoes). With a sostenuto pedal, neither modification is necessary.