Yes. You can easily do that. you need to create a hierarchical block and link you complete schematic to this block. You also need to define interface port on your complete schematic. These port would be considered as pin of top level symbols. refer parts in Data Convertor library (tools\capture\library\pspice\dataconv.olb) in your installation for example of this types of parts. This process works very similar to ADE/Spectre.
Other alternate method would to get the complete schematic netlist, manually add the subcircuit definition (example below)on this in any text editor. Save this as .LIb file. Open this .Lib file in Model Editor and Create symbol for this.
.subckt NAME_OF_SUBCKT Port1 Port2 .... PortN
<You schematic netlist >
.ends