I have done it by creating a <asp:PlaceHolder > object in by main module then loading the 2nd module I want into that.

Codebehind in main module C#

string controltoload;
PortalModuleBase module = new PortalModuleBase();

controltoload = "..\\SOME_MODULE.ascx"; //the correct path and filename

module = (PortalModuleBase)this.LoadControl(controltoload);

module.ModuleConfiguration = this.ModuleConfiguration;
module.ID = System.IO.Path.GetFileNameWithoutExtension(controltoload);

this.ID_OF_PLACEHOLDER.Controls.Add(module);
 

Matt

Thank you Matt