How do I play this part

I’ve learned to be pragmatic in places where your hands can’t reach. As Dominic Cheli pointed out, you could roll the chord very quickly—although that risks taking away from its power as well as the rhythm, and it also sounds rather conspicuous. This is similar to m. 16 of the Hammerklavier Sonata, where Badura-Skoda taught me to leave out one of the lower notes of the right hand chord. My hands are large but I can’t reach Beethoven’s chord without either awkwardly arpeggiating it, losing time, or compromising its power. (Liszt’s chord is comfortable for me so I play it as written.)

Sometimes you can respell a chord. In this case, maybe try playing E-flat with your thumb? This would give you more power than only playing the upper two notes of the right hand. (In that case, you might even try playing C instead of E-flat in the left hand chord to preserve the harmony.)

It may be worth noting that as of a certain point in his output (I can’t recall the year), Liszt notated tenths with an arpeggio sign.

A crucial point that mostly gets overlooked in this passage is that the main theme is in 5/8 meter! Many players inadvertently turn it into 6/8 by taking too much time for the leaps. Liszt quite often has unwritten temporary changes of meter, including elsewhere in these pieces.

If you're interested, I recorded the Transcendental Etudes on a Bösendorfer 280VC and released a selection set to Lord Byron's poem “Mazeppa.” This piece starts at around 13:30 in the video.

though I am not working on this piece at the moment and have barely sight read through it once, I would personally rapidly roll this chord as it still needs power, speed and accuracy, but the harmony will be very empty without the third. 

I just tried the various suggestions at the piano and found that playing E-flat instead of C with the right thumb and, in the left hand, C instead of E-flat works very well. The full harmony is there and it goes by fast enough that no one is likely to notice.

Arpeggiating the chord doesn’t sound very good to my ears, as it really calls attention to itself; plus you don’t get as much power.

Maintaining the harmony while changing the voice leading to accommodate a smaller hand is, to my ears at least, the best option.

I did some more digging, and it turns out that all editions I could find (on IMSLP) had the same tenth, but the 1837 version of the piece has a different voicing of the chord and previous chord, putting the lower notes of the chords (d and c) up the octave, and having a lower e-flat to make the octave.