how ro save 1 bpp bitmap using c# WinCE 4.2 Compact Framework 2.0

This post concerns creating a bitmap in Windows CE 4.2:

I would prefer using PixelFormat.Format1bppIndexed, but this PixelFormat is
not supported by CF. I need to save a captured signature with the filesize
reduced to a minimum to suit our clients needs. It does not matter if the
bitmap is displayed with higher PixelFormat, because only the data export to
the server is needed.
When I save this signature to a bitmap file, the file size should be less
than 2kb. If using a graphic object native to CF calling Bitmap.Save, it is
>32 kb. Hope, someone can help me.

Thanks.