After doing some further research in the NASA photo archives I discovered the hatch actuator is actually a round socket containing a square peg mounted near the collar of the docking mechanism. This correlates with the location of the interior hatch actuator handle being on the body of the spacecraft and not built into the hatch itself.
It can be seen in this photograph of Progress 55 (mechanism at the 1 o'clock position just inside the double o-ring seal:
And in this photograph from expedition 26 showing how it appears to the crew onboard the station (mechanism at the 5 o'clock position):
Also visible in the above picture are two holes in the drogue cover (AKA the 'passive docking unit cone') which supports a 'hatch tool extension'.
The hatch opening procedure is described on page 39, section 5.2 of the Russian Segment Operations 2A.2B Flight document (PDF) posted on spaceref.com:
5.2. PROGRESS-СУ HATCH OPENING
Hatch tool→РАБОЧЕЕ ПОЛОЖЕНИЕ (Working Position)
Fully insert hatch tool extension into socket ГЕРМЕТИЗАЦИЯ КРЫШКИ (hatch actuator)
Secure hatch tool extension on SM passive docking unit cone
Fully insert hatch tool into socket on hatch tool extension
Rotate hatch tool in the direction of arrow ОТКРЫТИЕ (Open) until it clicks (6-7 turns)
Stow hatch tool and hatch tool extension into СтА accessories kit 11Ф732.Г4000А1-30
Open hatch and secure it in open position
Report to MCC. MCC-H⇒MCC-M
This photograph from expedition 40 shows Alexander Skvortsov actuating the hatch opening mechanism of ATV Georges Lemaitre. The hatch tool extension is similar to a ratchet extension bar and is held in place by the two holes in the drogue cover. The hatch tool attaches to the end of the extension and is rotated clockwise to retract the hatch latches. Pen marks are visible on the inside of the drogue cover which say "open" and "close" in russian.
There is also a silent video from expedition 26 showing the opening procedure of the hatch of AVT Johannes Kepler:
Soyuz capsules have this actuation mechanism as well, so it is possible to open the hatch from within the station without the assistance of any crew aboard the spacecraft.