Have you tried piping it raw?
Code:
"F:\avs2pipemod\avs2pipemod.exe" -rawvideo %1 | "F:\codecs\video\X265\x265.exe" --input-res 1920x1080 --fps 24000/1001 --input-depth 16 --output-depth 10 --dither - -o "%~dpn1_10bit.mkv"
Aside from the Windows CMD syntax, this should work, just replace what is necessary. Also please excuse my use of avs2pipemod as I do not use avs2yuv64.