It sounds like you want to be able to show connections to custom panels in the Block Schematic view and then generate cable schedule reports from those connections.  (Note: I put this down because it's important to understand the actual problem you're trying to solve.  The correct solution to a problem may be very different from any preconceptions or assumptions you've made.)

In the Block Schematic view, reportable connections must be made to an I/O stub on a Symbol.  The I/O stub generates a 'Connector' object at the point where it touches the red outline of the symbol, and it is this connector object that allows rubber-banding (where the cable/dogleg follows the symbol if you move it) and reporting to work.

Therefore, in the Schematic environment you need to create a symbol that represents your panel with one or more I/O stubs.  You could do this using the Symbol Wizard, or by drawing it from scratch, or by editing existing Block Schematic symbols.  Once you have the symbol with I/Os you will be able to connect to it and generate reports.  Note: you can embelish the symbol in any way you see fit, and this could include adding the Panel Layout view of the panel (scaled and/or modified in other ways), but such embelishments won't impact on the core functionality that you're looking for.  The only thing that matters from a functional standpoint is the I/O stub/outline relationship.

I hope this is helpful.