Go to Sears, (or some other hardware/tools/in-depth hardware type major store. Minor ones won't carry the laser levels, nor the mounting blocks.) Look for their laser level mounting blocks: They have both magnetic bases (on the horizontal and on the vertical legs) and "pin point laser bases that can go into wood. Concrete? Might need an "adapter for the adapter, but ....
I've got a couple different types, will provide a photo if that will help get you some ideas. These laser mounts look like "L" - some have a variable height adjustment feature, some allow the laser to rotate, some just attach to the wall or vertical piece of steel that you want to use to mount the laser level. A theodolite is heavier than a laser level, probably needs to be more securely fastened than a self-leveling little plastic box that is only a few ounces, but .. try it.
Of mount a vertical angle iron (maybe 3x3x1/8 inch, or 4x4x1/8 to the concrete, then use a magnet to fasten the small "platform" to the vertical angle iron as convenient.
Do you need the centerline of the theodolite at that distance from the wall?