I was able to do the negative side of the op amp fairly easily, but I can't figure out how one would do the positive side. Below is what the circuit looks like so far.

![schematic](https://i.stack.imgur.com/BEiWs.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fBEiWs.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)

Edit: Only one op amp can be used.