to use parameters in aliases, i use this method:
alias myalias='function __myalias() { echo "Hello $*"; unset -f __myalias; }; __myalias'
its a self-destructive function wrapped in an alias, so it pretty much is the best of both worlds, and doesnt take up an extra line(s) in your definitions... which i hate, oh yeah and if you need that return value, you'll have to store it before calling unset, and then return the value using the "return" keyword in that self destructive function there:
alias myalias='function __myalias() { echo "Hello $*"; myresult=$?; unset -f __myalias; return $myresult; }; __myalias'
so..
you could, if you need to have that variable in there
alias mongodb='function __mongodb() { ./path/to/mongodb/$1; unset -f __mongodb; }; __mongodb'
of course...
alias mongodb='./path/to/mongodb/'
would actually do the same thing without the need for parameters, but like i said, if you wanted or needed them for some reason (for example, you needed $2 instead of $1), you would need to use a wrapper like that. If it is bigger than one line you might consider just writing a function outright since it would become more of an eyesore as it grew larger. Functions are great since you get all the perks that functions give (see completion, traps, bind, etc for the goodies that functions can provide, in the bash manpage).
I hope that helps you out :)