Select a Sidebar from Page Creation

Sounds like you could use page templates for this. You’d create a file in your theme called ‘page-services.php’ (for instance). When users create new pages, they’d select the “Services” template, rather than the “Services” sidebar, but it’s basically the same thing for your purposes. Here’s how to set up templates: http://codex.wordpress.org/Pages#Page_Templates

And here’s the conditional you could use to determine which template is being displayed (for use within your sidebar.php to swap out between sidebars): http://codex.wordpress.org/Conditional_Tags#Is_a_Page_Template

Hope this helps, best of luck.