... Are you suggesting the way to pull off a slider shot is to zoom whilst sliding to keeo the slider out of shot...? Would that not defeat the purpose, or at the very least give you a completely different looking shot to the standard slider shot you're apparently looking for..?
A zoom is essentially a kit of primes bundled into one lens. If you stick on a 50mm prime, you likely won't see the slider (depending on how far in front of the camera it is), especially if you're angled slightly up. If you stick on an 18mm, you likely will see the end of the slider, though again if your shot is angled up, you could frame the slider out of the shot if you really needed to have an 18mm lens on.
FWIW, I shot a really long dolly-in on a low-budget short film quite a while ago now, we were shooting S16 and were using roughly a 10mm lens IIRC. I had a dolly grip pushing me along, and to ensure that I got the framing that was wanted, as well as keeping the dolly out of shot, I reframed slightly about halfway or so down the track so I kept the thing framed as the Director wanted, especially towards the end but also never saw the track. You could only tell there's a slight tilt down if you were really looking for it, and either way it wasn't a distracting tilt that would look out of place anyway.