Sure.
Please remember that calling several ads using this method might load your server significantly.
All you have to do is go into your OpenX control panel, choose 'Direct Selection' from the left menu, next select javascript invocation from the options and adjust the script according to your needs.
All my banners have unique identifiers so it's pretty easy to target them with a simple '?what=' condition in the script.
The final script version is copied to where ever you want the banner to show, usually placing it inside one of the ad templates is a good idea.