Query Pane Docking in pgAdmin3
There is no way to do that. The only panes available in the main window are listed in the menu under View: Object browser, SQL pane, Tool bar.

You can ...

... select a passage in the query tool, then hit F5 to execute just the selection. This way you can have various queries on a page for ad-hoc calls.

... Copy SQL from the main window to query tool automatically with this option.