1. Put multihome in your path (i.e. ~/bin)
2. Depending on your shell, put the following at the top of its initialization
file.

CSH (.cshrc):

setenv PATH ${HOME}/bin:${PATH}
set MULTIHOME=`which multihome`
if ( -x $MULTIHOME ) then
    # Destroy environment
    env -i
    # Resassign HOME
    eval `$MULTIHOME`
    if ( "$HOME" != "$HOME_ORIG" ) then
        cd $HOME
        source ~/.cshrc
    endif
endif


BASH (.bash_profile):

export PATH=$HOME/bin:$PATH
MULTIHOME=`which multihome`
if [ -x $MULTIHOME ]; then
    HOME_ORIG=$HOME
    # Destroy environment
    env -i
    # Resassign HOME
    eval `$MULTIHOME`
    if [[ "$HOME" != "$HOME_ORIG" ]]; then
        cd $HOME
        source ~/.bash_profile
    fi  
fi