If you have the bottom of the forks cushioned with something soft on the ground (old towel etc),
you can usually push down on the whole bike and jump the forklegs up enough that the thread can be started.
This relies of course that the bike is no longer up on a hoist or milk crate, etc, or that the centrestand is tied off so it can't retract.
Having the bike tied off to something overhead may also be desirable, to prevent it tipping sideways and outta control.
I've also heard of folks using a tie-down ratchet strap, to pull the whole assembly up into the yokes.
It is also possible to make what that special tool may be - all you need is an old top fork nut thread ( cut off the hex), drill it and fit a length of rod to it,
with some form of handle, so it can be screwed into the tube and used to pull them up.
Bumping or ratcheting the tubes up seems easier, unless it doesn't work...