You can register your classic portlet trough the portlets.Classic
portlet, configured with a template and macro name, using an assignment
element in your portlets.xml file:
<assignment
manager="plone.rightcolumn"
category="context"
key="/"
type="portlets.Classic"
name="my-classic-portlet"
visible="1">
<property name="template">templatename</property>
<property name="macro">macroname-found-in-template</property>
</assignment>
See the Portlets section of the GenericSetup manual on Plone.org or the original PLIP for details on Portlet assignments and GenericSetup.
The properties match the portlet dataprovider interface, see the Classic Portlet source code for the interface definition for the Classic Portlet.