It sounds like you could make it work if you convert the non-GFCI outlet, the first one after the switch, into a GFCI and then run the rest of the loads from the GFCI-protected side. Your cable to the fountain appears to have the extra wire you'll need (red) for the photocell switch - this wire will become the hot for the lights. The lights will have to be hard-wired to the red wire (and also white and green in parallel with the pump) inside the compartment under the fountain instead of being plugged into the outlet that's there. You can't have both black (non-switched) and red (photocell switched) hot wires terminate on the same outlet, so hard-wiring the lights will provide the separation.
This all assumes that your pump is a 120V device and not 240V, otherwise the red wire would have already been taken.