I have posted this as bug #193 under ACS Subsite for now.
Jarkko, I'm interested in the customization issue as well. Seems the best and most flexible way for now is to have subsites within subsites for each group of package instances you want to share a common layout, but that does strike me as a bit of overkill.
An alternative could perhaps be to change a given package to inherit, say, bboard-master instead of the default master, but then you would have to provide and/or duplicate the template pieces in question for *all* subsites on your site, including the root.
I wonder if there is a way to detect from within Tcl what type of slave we have been called from. That would be a way of customizing the layout on both a per-package and per-subsite instance without having to change the core package.
