Did exactly that a couple of weeks ago on my KTM950S - those gel pads are in the 'raw' state and are very sticky at the edges. They are also shaped like a tractor seat and need trimming to fit an average enduro seat. I managed to trim and re-stick mine into a long rectangle shape. The suppliers recommend using cling-film or similar to seal the edges, indeed that's how it arrived with me but I don;t think that the film will be durable enough to take the use it's likely to get on these types of bikes. In my 'box of things going to be useful sometime...' I had some heat-sealing silicon rubber film which is normally used to seal and waterproof wheelchair seat cushions - no durability worries there then! Anyway, the re-trimmed and re-sealed gel-pad was ready to go on the seat pan.
I'd previously tried to soften the seat by drilling cores out of the appropriate area - this has been partially successful but was still not too comfy. I put the pad over the foam base, marked the outline and cut down about 20mm with a stanley (hobby) knife. I found then that I could simply 'pick' chunks of foam from the outline and soon had a reasonably smooth and even excavation. The gel-pad was a pretty good fit in the cut-out so I didn;t bother trying to stick it in or anything, just refitted the cover. So far the gel pad hasn't moved and doesn't look too bad - the outline is visible, but it's a small price to pay for a huuuuge increase in comfort!!
My invoice was a shade over £45.00 when postage and VAT was added, but with the reputation of the KTM factory gel seat being only marginally better than the wood-foam they use as standard I was happy to take the chance. It worked ..
I wish my wheelies were intentional...