Nand gates you already have and they can take the place of transistors for now, so C's and R's would bring the most options at once. And LEDs, but those should be very easy.

If you are mapping the lines where each pixel has resistance and capacitance (presumably quite small values) could you add a new pixel type with editable resistance / capacitance and hide it behind a graphic of the schematic representation (i.e. the zigzag of a resistor like --\/\/\-- or capacitor like --|(-- ?

Your current algorithm would need to be able to accept a wider range of values but it seems like it would work from a math standpoint.