Three signals are needed for the UPDI programming of the newer Atmel AtTiny controllers. The signals are available at the ICE AVR connector pins
Open the ICE case by pressing a screw driver into the side slots.
The VTG and GND wires can easily be soldered directly to the connector pins.
The UPDI wire can be soldered to the green transient protector, number three from left in at attached image.
I pulled the wires out and soldered to a 0.1" connector, the standard UPDI connector pins are
VTG is target voltage supply sense input only, the ICE cannot power the target.