Point motors can be fitted retrospectively providing your baseboard surface is not too thick. Peco solenoids or the slow acting point motors can be obtained with long pins that will go through a thin (1/2 inch) board. Fitting them to the underside of the board is not so easy but possible. You will need to drill a space for the pin to go through and slide. It doesn't need to be a large hole more of a thin long slot. You could achieve this by drilling several small holes in a line and then joining them up. With a thin baseboard this will not be too difficult. Of course you will need to drill through very carefully so that you don't go through the point as well.
Hope this helps.
Hope this helps.