There's no need for WIC. It's built into the core of Windows itself in the form of PlayEnhMetafile.
So, to get the picture into a BMP, you select your BMP into a DC, then do PlayEnhMetafile on that DC, and the result will go into the BMP.
Note that this isn't really converting a metafile into a BMP--it's rendering the metafile into the BMP. That is to say, a metafile is (usually) resolution independent. For example, it may specify a line from logical coordinate (0,0) to (100, 100). When you render that into a BMP, you get the line rasterized at a specific resolution. If you later wanted the same picture at higher resolution, the metafile could provide it, but the rendering in the BMP couldn't/can't.