I wouldn't be too worried about the oil supply to the bearings. As you all know the oil/air mist distribution within the core-engine works ok already, if the afterburner would cause too much back-pressure to disturb this I reckon the entire engine operation would stall. The whole engine operation principle depends on small pressure variations between impeller, diffuser, combuster outer area and hence into the combustor. (Not by mass-flow as some might think....although you need that as well for power...
) Outside the bearing shaft tunnel there is a little over pressure to keep the cooling air going inside the tunnel together with the supllied fuel/oil pressure, would this fail due to back-pressure, the entire engine wouldn't work at all as the other factors mentioned would stop their operation as well. I would be more worried about the EGT rise which would occur, that has to be monitored at all times as the rear bearing is housed directly below the hot section of the engine.
Following this with great interest, keep it going Smithy!
Rgds,
gerald