I normally do like many people here, which is just wipe on a thin coat of oil and burn it off on the stove-top (covered in aluminum foil to reduce oily residue on kitchen surfaces) when I think the seasoning needs an extra touchup beyond what it gets from cooking. Years ago I tried the oven trick, but as you say it's just not worth the bother. Plus, it can really dirty your oven and your whole kitchen.

But last year I had the idea to season the pan on my Weber coal grill.[1] And it worked extremely well. On the grill you can season both sides and the handle just like in the oven, but without worrying about the sticky residue it creates everywhere else. You can get the pan much hotter than in the oven, and more evenly than on the stove. My IR thermometer measured the my pan at something over 700 degrees fahrenheit on the grill, which was about as high as I wanted to go.

My pan was purchased unseasoned and the seasoning I managed before trying the grill was spotty, uneven, and prone to flaking. After about 15 to 20 minutes (or maybe 30? I don't remember precisely) on the grill the seasoning was perfect on every surface--as shiny as fresh oil, but completely dry. I applied one really good coat of oil, enough as I could manage without it pooling and creating runs, and wiping off any excess that pooled as the pan heated. The primary reason you normally season with thin coats of oil is, I think, to ensure an even, consistent surface. But on the grill you can wipe off any excess as it pools, so you can apply a much thicker coat in one shot rather than bake-on multiple thin coats.

For no good reason I stupidly tried to season the same pan on the grill a second time several weeks later. The second time I was lazier and less cautious and managed to burn off some of the existing seasoning, as well as letting too much oil pool and run in some spots, which became prone to flaking. But in neither case was the seasoning ruined all the way through to the iron. That's the danger of doing it on the grill, I guess. At 700 degrees you don't want to keep the pan in there too long as it'll ruin the seasoning--pools and runs will quickly harden, leaving an uneven surface that even wooden utensils can end up lifting, and hot spots can get much hotter than you'd want. I think at somewhere around 900 degrees seasoning will just completely burn-off in short order.

The only discussion about seasoning pans over an open fire I found online involved someone recounting (himself or someone else) seasoning pans over a camp fire. IIRC the advice I read there was to be careful as at too high a temperature not only will you destroy the seasoning, but you can damage the cast iron itself, either cracking it or changing its thermal properties. But with an IR thermometer, a spray bottle of water, and some coals you can get an amazing seasoning in one shot in under 30 minutes, and then grill lunch.

[1] It came to me sometime after I got the idea to fry chicken on the grill. I like making pan-fried chicken in my cast iron pan, but my wife hates the mess. (I hate the mess too, I just like the fried chicken more.) Frying on the grill works pretty well, but controlling temperature is difficult, especially because it's not easy picking up a large cast iron pan from a hot grill to reposition hot spots or to be able to spray some water over the coals. (Or maybe I'm just a wimp.) I'm still experimenting with technique, but I've yet to have an out-and-out fail.

And, yes, I keep a large ABC-rated fire extinguisher nearby, as well as some small foam extinguishers for stove-top fires so I have options and don't hesitate.