Standard cabinets usually have the drawers that slide into the frame of the cabinet as shown in the first pic (further down).

If it were this type, I could put the bar on as shown....no problem (pic taken from Major Manufacturing website)
This shows the front of the cabinet.

This shows an angled view....where you can get an idea of my predicament...

View with top drawer open, showing sliders on drawers...

View looking at top drawer fitting into frame....not possible to secure both drawers simultaneously here...

View between bottom drawer and top drawer, showing cavity between cabinet frame and where the edge of the drawer is.

The client wants to lock both drawers simultaneously if possible. I originally thought of using PPL's (Push Pin Locks) with an extension pin, rivetted to inside wall of frame and extension pin slotting into drawer wall. 2 locks on each cabinet. Lock Focus in Australia make some master keyed versions that would be suitable.
The client is an international air freight company, so shipping them from any international location will be done at their cost (yipee) if necessary.
Because of the quantity of eyes in this forum, someone might be able to determine a possible solution that I cant see.
Thanks.