On the question of supplying plants for your bank, to grow indoors, let me just say it's going to be a big headache for you, David.
If they cool it excessively in the summer, and heat it too much in winter, then the air is just generally going to be very, very dry. Something like a succulent - Sanseveria comes to mind - is the best bet for a plant that might stay good looking for more than a few weeks in that environment. But, also every plant needs good light to keep healthy and growing. Do they have big windows or skylights at the bank?
About "late blooming" flowering plants: usually perennials like celosia and chrysanthemums come to mind. They fill in the late summer, into fall with some nice flowers, then generally die back almost to the ground, stay dormant through winter and jump right back up in spring, making an ever-larger clump. They're great value in flowering plants.
There are a few flowering plants that will go though winter, still putting up some flowers. Pansies come to mind, but they will fade out and possibly die in the hot, dry summer weather where you are.
Most people start seeds of perennials in the fall, for earlier bloom in the spring. But if you want to keep seedlings going through winter it takes special care, the right amount of watering, and protection from frost. This can be supplied easily if you don't have too many cold nights. Something as simple as a cardboard box put over the plants for the night will usually keep them from frost damage. Here, I drape my tender plants with special 'frost cloth' that breathes a bit, but traps enough heat rising from the ground to keep the temperature at least 10deg. F warmer than the outside air.
I usually remove it for the daytime to let the plants get maximum sun benefits, but probably have to cover everything about 5 nights per winter. We also have good humidity here most of the year, which also helps moderate the cold damage to plants.
