Ok, here is a hack:
Each of the Port Pins, A, B, C can take on three states: High, Low, and floating (TRIS set to input). They are used one at a time; If using A, set B and C to input mode, etc. A low-high makes +1.5V and -1.5V across the load R9,respectively . B makes +2.5V and -2.5V. C makes +4V and -4V. Resistors R1, R2, R3 ratioed against R4 is what makes the specific voltages you wanted (poor man's non-monotonic DAC).
If A, B and C are all floating (set as inputs), the voltage across R9 is zero. R7 and R8 make a Vdd/2 floating ground.
The OpAmp can be any modern CMOS 6V rail-to-rail type which is capable of sourcing/sinking 15mA.