It does look like this is not doable.
Actually it
is doable though not easy. It would require a proxy 64-bit DLL that would relay the actual tasks to a dummy 32-bit process having the original 32-bit DLL mapped into its process memory, using
inter process communication (a.k.a. IPC) facilities such as sockets, pipes, or COM. That would of course imply perceptible speed penalties and may be even more laborious than re-writing the original DLL for native 64-bit compilation.
