The alarms in Picolog software can only control the digital outputs. Yes you need to use a transistor/Solid state relay that would switch on with 1.5mA or less.
The digital outputs 1 and 2 on the DrDAQ can be set as PWM outputs. But you can only control these with the PicoScope 6 software or the SDK.
The DrDAQ, PWM outputs with resolution of 1us and the period can be set to 65535 µs or less.
Using low pass RC filter on the output will convert this to dc voltage.
A period of 65535 µs is around 15Hz, a filter capacitor on the output would need to be a large value, say 100uF, as there is already a 2k2 series resistor.
In picoscope 6- I set the period to 1ms (1kHz), and connected a 1uF cap on the output, I had still had 500mV ripple voltage, you may want to use larger value.
At 1ms period you still have 1000 steps in voltage level. You would need to buffer this output to drive anything that draws current.
You could try using the alarms feature in Picoscope if you wish to control the PWM O/P.
NOTE: If you are using PicoScope software you can only set the duty cycle from 0-100, and not say 50.2, so there are only 100 steps. You can then set the period to 1us, and you will have no ripple will a 100uF cap.