The advanced editor isn't actually that bad. If you don't want to touch the scripting, then you can leave it mostly alone and it works pretty much the same as the basic editor. I can't script worth a damn (beyond putting in pictures!) and I haven't run into any problems yet.
So yeah, if you want centered pictures, convert, then you'll see the <>Source button. Copy in this:
<image align="center" src="IMAGE URL">
and voila, you should have a centered image.
Although, sadly, you'll have to do this again every time you save. At least, my advanced editor deletes my pictures every time I open up the page again.