It could indeed. I worked out a lazy hack though. I ordered some feed through capacitors from eBay so will deal with it later, but for now I have fed the +V in through one of the screw holes on the BNC. It'll do the job nicely to be honest. It's done for now
I have plugged into into the GDM-8341 and programmed it (joy to programmable DMMs) to do a Y=MX+C transformation. I've written the M and C values on the box unceremoniously with marker. If you stick it in "math" mode and plug them in it will read dBm from -90dBm to +13dBm directly off the meter screen with no calibration curve or lookup chart required.
Edit: add picture of final device:
Building your own test gear is as fun as buying it and fixing it
BOM cost on this was about £7 thanks to eBay mixed lot of junk, China, Tayda and quality stock control at RS.
If I was to do this with parts bought new from RS I'd be down £60 or so (mostly being mugged for the Pomona box and the AD8307).
If I was to buy an HP with working power sensor I'd be down £200