I would recommend to do that with some offline batch resize tool - there are surely lots of them from Photoshop to smaller tools - as otherwise in any case the server has to do the work.
Yes, there will obviously be a lost in resolution, but at least uploading won't be blocked over a configured size and files/images do not need to be resized manually.
If w"configured size" refers to the filesize upload limit lots of servers have you won't be able to workaround it this way as you have to upload it before it can be resizes by Zenphoto (=server.