Editor UI: Inserting entities

This isn't strictly game programming related, but I think it still fits.

I'm trying to decide on a nice way to let users insert entities into worlds in Clockwork. Suppose the user tries to add a staticmesh entity. Should there be a pop-up that allows the user to specify what model and shader file to use (these are basically the only properties required to add a staticmesh to the world)? Should it display a new panel in the main window? Or should it just create a sort of "placeholder" entity, that isn't really active untill properties are correctly set in the property view box (which is always visible in the left pane, for nice dynamic property editing)?

I'm trying to avoid pop-ups as much as possible, but in this case i'm not really sure if it can be avoided.

At the moment, i'm leaning towards the display of a new panel, but i'd like to get some of your thoughts. Also, if you have any other ideas of how this could be done other than the ones I've mentioned, feel free to offer them up.

How about combining all of them?
If you create an entity, a property editor will pop up, unless you SHIFT+create the entity, in which case it skips the pop up window, and leaves you to edit the properties from the view box.

I like the idea, but unfortunatly now i'm not sure if I can get the placeholder entity thing to work properly with the current system. I'll keep it in mind though.

What I did decide to do, was combine the pop-up and panel idea, rather than the pop-up and placeholder idea. Basically, when you click the button to add an entity, it displays a borderless window (which looks like a panel) at the location of the mouse cursor. From there you can edit the initialization properties, and continue to add the entity to the current world.

Comments?