You should be able to take a direct train from Lugano to Goeschenen, which is just on the north side of the Gotthard train tunnel, and from there connect onto the Glacier Express up to Andermatt. For there trains go down to Brig through the Upper Valais (Goms region), and from Brig you head up towards Zermatt. You'll have to check the SBB website for schedule details. You might be able to do it with one or two changes, but I'm not sure.

Alternatively, you can head to Locarno and take the Centovalli train through to Domodossola (very nice) and then take a train to Brig through the Simplon tunnel and connect onto the Glacier Express there.

Perhaps you could travel there one way and back another?

Heather

PS:

You can do this on the RhB trains going through the Albula pass. The catch is that your 'destination' has to be Samedan. Not sure about what others there are.