Unfortunately, it is not possible to have imageClickMode be NAVIGATE and OPEN_URL at the same time and SimpleViewer uses the same value of imageClickMode for all images in the gallery.
It sounds like what you are trying to do might be very difficult to achieve (if possible at all).
Perhaps a possible workaround would be to use captions for certain images and have the captions be links to your custom pages by using HTML formatting as noted in this FAQ:
How do I add HTML formatting to my captions?
... it needs to be centered, vertically and horizontally.
If you need to place image captions in a location not supported by the captionPosition configuration option, then you might like to try using a Fixed Layout. You can specify the exact dimensions of the gallery and the position of the captions in pixel values (relative to the top-left of the stage).
For reference, all the Fixed Layout configuration options can be found here.
Please also see the Fixed Layout note in the SimpleViewer-Pro Layout Guide here.
SimpleViewer Support Team