The weeping disectums tend toward pendulous growth because of genetics, so the only way to establish a new leader is by mechanically manipulating an existing branch to a more vertical orientation; or, you could do a thread graft through, or an approach to, one of the more horizontally oriented branches. Both are relatively easy and require little skill or knowledge.
After another look, the best way might be by tying one of the suckers growing in the crotch of the top branch to the stub to keep it vertical. This image should help:
Leave the stub as is for now. It will serve in the stead of a stake to tie a branch to. If there is no suitable branch now, be patient. As long as you keep the tree healthy, spring will bring forth a good many opportunities to give your tree some additional ht.
Al