You don't need a hardfile, WinUAE handles non-Windows file names internally. Just make sure you use AmigaOS utilities to unpack the LhA archive, don't use WinRAR or similar.
If you use UnArc, you also have to make sure to have Boinbag 1 installed because the first version of UnArc cannot handle file names with spaces, either. Better use the original LhA program to unpack the archive.
Bye,
Thomas