Decoding HEVC with Alpha Channel via NVDEC: Monochrome (4:0:0) Workarounds?

I’m working on decoding HEVC streams that include an alpha (transparency) channel using NVIDIA’s NVDEC. The alpha channel is encoded in monochrome (YUV 4:0:0), but NVDEC’s HEVC decoder appears to lack support for monochrome formats. How can I work around this limitation?

Like somehow force the pixel format 420 and then do postprocessing ?