I have been tinkering around with solo rules for SA, and so far I have tried the following:
Using a card system for activation: each figure has a card and gets to move when drawn. If a leader type is drawn before minions/fodder types they can activate the lesser figures as per the rules (and the lesser types don't get to move when their card is drawn, as they have already moved), otherwise any figure can be activated when their card is drawn - no need for a leader to activate them.
The turn can end early with the use of a "End turn" card - any figures not yet activated loose their turn, which can balance out the activation of all figures.
Random events are included in the deck if wanted.
Lurker actions - will attack the nearest agent, or attempt to obtain a goal - they will attempt which ever is closest.
So far it is working rather well and games can be a bit tense when a turn ends before you get to activate your favorite agent. The randomness of the cards removes the predictability of a solo game.