You can edit the line in the WD.ENV file, the original of which is shown below.
**************************************************************************** Project and drawing-related paths and settings
***************************************************************************
WD_PROJ,%WD_DIR%/proj/,AutoCAD Electrical default project data folder
You can change to be like this (with your own drive letter):
WD_PROJ,H:/PROJ/,AutoCAD Electrical default project data folder
You may also need to put this (H:/PROJ) into your File Support Search path. Be certain to make a backup copy in case ACE replaces the file.