how can I add command line parameters to an application shortcut
Make an Automator app called "ChromiumLauncher" that runs the commands you want. Drawback is you will get the ChromiumLauncher bouncing in your Dock for a second or two before it goes away.
It will launch faster if you cut out Automator and just do it with Applescript (and then save that applescript as an application bundle).
Here's an example:
do shell script "open /Applications/Chromium.app --args --enable-expose-for-tabs"