It might be possible to insert them anywhere but I've made the explicit choice to force them into managed subfiles. Mainly because these are flexible parts and therefore should be handled like any other part inside a model. The alternative would be to handle them like special groups but I felt that's misusing the nature of grouping somewhat.
Anyway the upcoming nested editing feature will probably resolve / ease your placement issue with this particular model.
Anyway the upcoming nested editing feature will probably resolve / ease your placement issue with this particular model.