I can think of some possible scenarios. Now that I think of it, what does "wise" mean in a solitaire game? Ending the game as fast as possible? Ending the game with at most VP as possible?
1: (does not work for Saboteur) You have 2 quarries in play, at least 10 buys, 2 piles are empty and these are the unique cheapest action cards available. Then you can piledrive them.
2: You have forge/forge on top of your deck. If you can topdeck a $4-cost card with watchtower, you can forge a colony.
3: Let's do something far-fetched:
-You have a watchtower in hand
-You have 2 quarries in play, but no other +coin or +buy cards
-Nomad camp is in supply, but embargoed 10 times. (don't ask me why in a solitaire game)
-The Watchtower and conspirator piles are empty, and there is 1 colony left.
-You want to end the game with 1 more colony in 1 more turn.
-The kingdom doesn't have action cards except Thief, Pirate Ship, Saboteur, Sea Hag, Watchtower, Nomad camp, Conspirator and $7+ costing cards (the first four are not all needed in the kingdom, 1 of them is enough)
-You know that the top of your deck is: University, Conspirator, Platinum, Silver, Colony (in this order; you can know this if you just played Navigator or Cartographer, or just topdecked 4 of these cards).
Now you can buy any of the cards in {Thief, Pirate Ship, Saboteur, Sea Hag}, topdeck it, and then the following turn you can play university (gain nomad camp on deck), play the action card you've topdecked and play conspirator, draw nomad camp, play it, and reach $11 to buy colony.
As far as I see there's no other way to do this, because you can't buy the nomad camp since it's embargoed, you can't buy silver, because you just have $2 to spend, and you can't buy another action card.
@heron: with vineyards they're indeed viable sometimes, but with gardens it's not easy to come up with an scenario where you wouldn't have bought copper/silver instead, and with conspirator it's not easy to make them viable either. Playing a conspirator dead is about as good as playing a Thief and then playing a conspirator "alive". In fact, my third solution was the easiest I could think of using conspirator.
EDIT: another scenario: You have watchtower in hand, and you know you will have death card in hand on your next turn (and ruins are empty)