You can't get rid of the space. You can put a comma there, but it will have a space. The only way around that is to make a custom channel window for yourself that shows it without the space. Of course, that has no affect on what others see... and I personally don't think it's worth the effort just to remove a space.
As a note, if you put a comma, people understand even with a space.
* Riamus , something.
Speaking of which, when would you actually use a comma after your own nick in an action? I'm sure there's something out there, but I can't think of any. I can see using 's or whatever after your nick... but a comma? Sure, you'd use a comma after someone else's nick, but your own? Again, I'm probably just not thinking of the right scenarios.