Yes, but only by paying that very expensive normal fare for the cash one-way, and buying a separate award ticket for the other direction.

You cannot do this on a single booking, so you wouldn't be able to get the deep discount cash fare that you'd like.

For what you want to do, I also think that the best thing would be to buy a cash WT+ ticket, and then use Avios to upgrade in one or both directions.

Note that you can't buy a WT ticket and use Avios to upgrade to WT+, except if you buy a very expensive WT ticket to begin with. The cheap WT tickets cannot be upgraded using Avios.