Reward Ticket Booking

I've had zero luck getting 2 UC for SFO-LHR-JNB next January, so I had sucked it up [8D] and used UAL miles for 2 F class on the SFO-LHR route, and was prepared to pay for the 2 UC tickets. But never one to give up I have been monitoring Expertflyer and the VS site to see if I would get lucky, and today I did. I managed to snag 2 UC Reward tix for the outbound, but there's nothing for the return. So I bought a JNB-LHR round trip planning to use the LHR-JNB portion later next year, I will have a year to use it so no problems.
It seems that the downside to the plan is that the taxes and fees are a higher for 2 one way reard tickets than they would be for a round trip, but given the overall savings, it's not much of a problem.
Better still I may be able to get the return journey as a reward ticket, then either keep the purchased ticket for a later date (within a year) or cancel it for a refund. Though there is a GBP50 penalty to do so, but in the context of my savings, it's nothing.
Anybody else use similar tactics?
It seems that the downside to the plan is that the taxes and fees are a higher for 2 one way reard tickets than they would be for a round trip, but given the overall savings, it's not much of a problem.
Better still I may be able to get the return journey as a reward ticket, then either keep the purchased ticket for a later date (within a year) or cancel it for a refund. Though there is a GBP50 penalty to do so, but in the context of my savings, it's nothing.
Anybody else use similar tactics?