actually jgpaiva's solution is basically correct -- you just need to update your alias result to SHOW YOU the : as well:
ejectCD $$1 | "C:\Program Files\SysTools\EJECT.EXE" $$1:
ejectCD $$1: | "C:\Program Files\SysTools\EJECT.EXE" $$1:
keep in mind this will not work on your example of "eject e f" since it will only add one : at the end of the f
but you could solve this by making another ejectcd alias which matches 2 drive letters and adds a : to both, but that would require a separate regular expression alias.
in this case, a better thing might be to launch a kind of batch file or script to invoke and do the replacement after the launch by this script. i urge people to use this kind of approach.