Then I think the idea of some big pots might be workable. Start watching your local swap meets and garage sales!
What about just filling up that bed with rock, and setting big containers with good soil in them on top of the rock? It would act like a terrace, the water from the containers would percolate down through the rock and dissipate somewhat, and when you get heavy rain that rock would act sort of like a French drain.
That's "The Real Solution" for a spot like that - a French drain. But you'd have to dig out enough soil to install the porous pipe so that it could drain out underneath the wall. An awful lot of work for you, or expensive to get someone else to do it. (I know, we had to install one all along a wall of the house the first summer we were here).
