Unfortunately the most you can do is to include or explude ALL cliparts via the
Exclude cliparts from hi-res option. Selecting specific ones is currently not possible.
However, for a scenario like the one you described (where I assume you'd manually add the cliparts you want with better quality), I would download by leaving cliparts and chekcing the
Include Items as Separate Layers option.
The files into the layers archive are already sized correctly and includes only one item each. This means that loading those into a single photoshop document will allow you to keep only the ones you need pretty fast (by using the
load images from stack option), and you can add your better images in a matter of seconds