I feel to have spent all my breaks at work interrogating station station staff about the priv oyster, nobody seems confident with information.
I now know that they can be issued, on a separate oyster to the staff pass but I have not found anyone working for the underground who has one or has issued one to another member of staff. The reason being that they are normally of very little value and usually more expensive to use than paper tickets, at least this is what I am told.
TFL staff are not normally going to reach caps and Oyster does not take account of return fares so it normally costs virtually double to make a journey, in my case 2 x £1.10 against 1 x £1.20, not really a satisfactory solution.
I am still waiting for a reply from my email to Southeastern, which I sent on Saturday, I will pass on their reply when I have it.
I don't think it will quite work out like that. Inside the zones, only Anytime fares remain on paper AIUI, so the return wouldn't just be pennies more than the single. Oyster PAYG is also generally cheaper so two singles on Oyster at peak time at worst would be comparable to the paper Anytime Day Return.
Waterloo East to Blackheath appears to be £1.85 return on paper, 90p Oyster peak single and 65p Oyster off-peak single, so you would be better off using Oyster. I think it works out more or less like this in most situations in the peak. Off-Peak Oyster would be cheaper.
I was just intrigued initially why you'd rather change at Southwark when getting off the Jubilee a stop earlier at Waterloo would give a similar result without the faff finding a place to pay for the ticket, but tbh I am more shocked that gateline plainly refused entry upon the presentation of a staff pass. They could have used a bit of common sense, but you don't get that these days with some gatelines I find ime.
I agree with the suggestion that equipping gateline staff at Waterloo East out onto nomansland with a portable ticket machine is a good solution, although now that they allegedly have a TVM there, I don't understand what is so difficult with issuing gateline staff an instruction that people requiring priv tickets to be allowed in and pay at the other end.
I don't see the relevance comparing King's Cross and St Pancras with Waterloo East and Waterloo, which operate very differently barring the fact that they are technically both separate stations, but I can't really be bothered with it because we will just be bogged down by technicalities. I would prefer clearer guidance being issued for situations like this, but I suspect there is more chance of SouthEastern putting a ticket office there than clear guidance happening.