Re: Setting custom tinyMCE configuration in an XBL control
Right now, you can't have a different config for different instances of that control on the page. For that to be possible, the code in tinymce.js (look for: var tinyMceConfig = …) would need be changed, and find the config from some other place (e.g. object indexed by the control id pointing the a config for that control).
I agree it would be good to upgrade to TinyMCE 4, but we don't have immediate plans to do that upgrade.