I can put a voltage divider where R2 and R3 are but I
have one concern. This would put a resistor in parallel (to DC) with R1,
which is between the gate of the MOSFET and ground. Will this affect the
circuit?

Chris-

Yes, it would appear to upset the bias on the MSFT1 gate. R4 is in series with
R2//R3 and R1. Current flowing through R1 develops a DC bias voltage on the
gate. You should be able to DC-isolate a new shunt resistor by wiring a
capacitor in series with it.

Try and keep added components away from the output side of the circuit, or it
could turn into an oscillator!

73, Fred, K4DII