Autodesk's Jeff Bartels explains how to employ a custom Numeric Generator PKT file to create a geometric transition in a subassembly without that targeting.
From the Jeff Bartels YouTube Channel.
and the Civil Immersion blog.
Jeff points out that it helps to know thy subassemblies in Civil 3D.
This is a sophisticated method to employ a fake profile, a PKT, and output parameters to produce a subassembly component geometric widening without supported targeting in the subassembly.
This method works to solve a one off problem, but perhaps you'd be better served to build a target included PKT if you need to do this a lot.
It is also possible to employ another Subassembly/PKT in the Assembly that has targeting support between the lane and the curb subassemblies as shown.
We still have the project problem of letting others know you pulled this rabbit out of the hat.
How do you inform other project users that the Assembly employs a strange PKT and output parameters in this way?
Previous post mentioned in the video on Share Assembly Output Parameters Between Subassemblies
The playlist link to Jeff's Quick Start video course on the Subassembly Composer.