You will have to set the WINEARCH and WINEPREFIX environment variables each time.
For instance:
env WINEARCH=win32 WINEPREFIX=$HOME/.wine_for_32bit winetricks mono28
If you only want to use 32-bit windows software, you can just recreate ~/.wine as 32-bit with the WINEARCH variable set to win32. Then put a statement into your shell's login scripts to set WINEARCH=win32 every time you login.