how about a 2x6 wall below the pipe and a shorter 2x6 above the pipe, that should give enough ledge past the pipe to notch the upper shorter wall around the pipe and still sit on top of the lower top wall plate ledge. for the long span use double top plates, 16' is average wall plate sizes- be sure and pick up straight lumber from the building supply. The other option is as oh'mike mentioned, the block wall insulation on the upper portion of block wall will need to be moved where you need to brace back to the concrete for the upper pony wall support.