Filtering options for a combobox

I currently have a log-on dialogue box which I present to users when they wish to log onto a target system. As I have quite a number of possible target systems, I offer them a combobox in which they can type the first few letters of their chosen target system. This currently looks like the following:

Some of these target systems have an attribute which means that the user does not need specify their password on connection (SSO), these are listed with a slightly different display name (in the example above, I have denoted it in brackets after the system name).

I was thinking to make things a bit easier for the users to select an SSO system, that I would add a checkbox to filter the list of system names in the combobox, so only SSO entries were shown, so something like the following:

The only issue with the above is that for some reason it doesn't look as intuitive as it could be (in my opinion) because as dialogues flow from left to right, top to bottom, you have to immediately go right to check the box, then left to choose your system.

Is there a nicer way to present this filtering option to users?