Without custom code, it is not possible to trigger an AU without updating the feature in some way. Generally you could use an unneeded field and just modify it, which will trigger the AU to run.
With custom code, you can create an instance of a specific autoupdater and trigger its Execute method, passing in the object that you want it to run on. For example, if I had a custom AU called "TestSpecialAU", I could do something like
var au = new TestSpecialAU(); au.Execute(myObject);
Where myObject is my particular feature as an IObject.
Keep in mind that this method is only executing the SPECIFIC AU that you specify in your code. In the above case, only my TestSpecialAU is firing. It does not execute all AUs assigned to that object.
Let me know if you have any questions!
That answered my question.