Just to add fuel to this option: Bernie Mikkelsen used to do a LOT of this steerer Frankenstein repair, and he did GREAT work for a low price...before he had a stroke (that's another story). How it's done: you cut the old steerer off ABOVE any butted section, nice and square, insert a short (3" or so) section of steel tubing that fits tightly INSIDE the steerer, then slide the new replacement steerer over the insert, half of it in each part. The gap between the 2 parts must be chamfered on both ends with a 45 degree "V", and then it's filled with a nice clean TIG bead, ground smooth and checked in a lathe for perfect alignment. With this method you can make any length you need, threaded or smooth, but I reckon that with adding a threaded tube you must be even more careful to keep it perfectly aligned. Seeing Bernie do it, I am convinced that it's best to trust this to somebody who knows the rountine and has done it alot...he made it look easy (and it was for him) but I know it would be a challenge for an amateur.
BTW, that greenie sure didn't look like a Fuji to me.