to answer my own question: make the file in your bin directory and link to it from /usr/bin and bash will find its name in the path:
sudo ln -s $HOME/bin/filename /usr/bin/filename

hey, surprise, didn't realise i'd get to comment so easily. but i had a wordpress account... Good show, launchin a linux toolbox :-) Like the "hard copy" graphics too...

#run fortune when you want it; mine's commented out in .bashrc
alias 4tune='mint-fortune'
# edit this .bash_aliases file
alias bal='vi $HOME/.bash_aliases'
# access a pen drive called disk
alias cdd='cd /media/disk'
# customise .bashrc
alias custom='vi $HOME/.bashrc'
# count down the days to World Cup Socccer's kickoff
alias fifa='expr 161 - `date +%j`'
# switch to GUI to open a file
alias go='gnome-open'
# use GUI to open the home directory; 'nautilus $HOME' is slower
alias home='gnome-open $HOME'
# quit firefox without the mouse notching up miles; also clean cache
alias kf='killall firefox'
# logout from the terminal
lgt='/usr/bin/gnome-session-save --kill'
# ls varies among distributions; show hidden files only
alias lh='ls -la --ignore=[0-Z]*'
# open Open Office Word Processor but skip splash screen
oo='oowriter -nologo &'
# see your internet data usage
alias ppp='ifconfig | grep --color 'RX.by.*\$''
# use python to do calculations or serious programming
alias py='python'
# shutdown the computer from where you are
shut='sudo shutdown -h now'
# open another terminal
alias tt='gnome-terminal &'
# today in history and more
alias today='grep -h -d skip `date +%m/%d` /usr/share/calendar/*'
# open an xterm; useful since it looks different
alias xt='xterm &'

what i was looking for was a way to run a file as root. eg. source ~/bin/file followed by "file" as root would work but i had sudo in mind.