How can I use Page editor for two separate templates?

There are quite a few ways to do this, here are a couple:

  1. Use a plugin to control which Widgets display on which Pages/Sections. This is a plugin I’ve used which works well. It adds a “hide/show on….” checklist to each widget where you can select where the widget will display. Works great, but if you have a site with tons of pages and page-specific widget content it can be a bit confusing to maintain.
    http://wordpress.org/extend/plugins/display-widgets/
  2. Either hand-code or use a plugin to add page-specific custom fields which you then display in the sidebar. The combo of “Advanced Custom Fields” and “Advanced Custom Fields Widget” works well here. You can add any kind of custom field panel (WYSIWYG editor, image upload, radio/select, etc) to the Page editor. Then put one Widget into the sidebar, and have it display that content on a per-page basis. This is probably the cleanest way to go IMO:
    http://wordpress.org/extend/plugins/advanced-custom-fields/
    http://wordpress.org/extend/plugins/advanced-custom-field-widget/

Best of luck, hope this helps!