Hi Dave,
From my expirience - Winbond's microcontrollers are cheap and
not too hard to buy .In Digikey Atmel 89S is cheaper, but with limited code space. Yes - noRealISP is problem. How we manage this :
1)I got datasheet for Parallel Programming - not very easy but
successfully . I have datasheet for 78E516B and 78E58B.
As far i remember there is only difference in signature (and flash size offcource). And pre-programming can be made by another 8052 , there is no need for 12V.
2)i reprogram my parallel programmer,based on at89c52 - we have at that time HiLo universall programmeer in working condition. You can do parallel programmer, using AT89S52, without buying universal programmer.
AT89S52 costs under 2USD (!!!!, but is only 8kB ..) , ZIF40 socket is about 13 USD in Digikey. And You will spent some time to build.
3)Last 7 years our programmer was used , 2..3 ZIF PLCC44 socket was changed in this time. Another way (which we used too) was to ensure parallel programming in system - we have in some our devices enough headers and connectors.

I'm still searching for Winbond alternative (with 64kB flash), and we still use our equipment.
regards