Creating AutoCAD P&ID blocks that include Schematic lines and inline assets

Please refer to image attached. We have blocks like the cooling tower (top figure) with just the piece of equipment. We'd like to add Schematic lines and inline assets to the block like shown at the bottom of the image. I know I can do this by creating a template file (dwg) which my users can add to the project and then copy or move data to appropriate sheet. I'd like to stream line this process a little more and have all the entities in a block. When I open my PSS (Project Symbol Style) Drawing to build the block and i try to add SLines I get error because drawing is not part of project and you cannot add a PSS to project. Is there a way to work around this issue and create block with assets or should I just use templates ?
Thanks for the help
KC