Cheap, dirty, probably not reusable....... Needed: An old shovel or rake handle made of wood. Find one fat enough to thread into the end of the tube, keep it as long as possible, then thread it into the tube and pull on up. Watch out for wood particles that may split off and fall into the tube-hence a dirty method.
More work, cleaner, and reusable.......Needed: old fork cap, threaded stock, washer, and nut, a beer can (unopened and ice cold), cigarettes.
Take an old fork cap and grind off the edges of the hexagonal part. Stop and have a cigarette. Then weld an 8 or 9 inch piece of 1/2" or so threaded stock to it. Then it's time for a smoke. With triple trees in place, thread this tool into the fork tube. Place the ice cold beer can against the upper edge of the fork tube for a few moments, then start to feed the tube into the lower triple tree. (The beer can may help to lightly 'shrink' the tube for easier installation.) Slide a big fat washer on that rests on top of the upper triple tree, then tighten a nut onto the threaded stock. This will pull the tube up into the upper tree. Once seated into the upper tree, remove the tool, put the cap on, have another smoke, and open the beer while realising that I was just bullshittin' about the ice cold beer can helping shrink the tube a little. Heck, you just busted your rear getting these tubes installed, it's time for cold one!