Pre-order-not Returning-send Download

Is it possible to do the following:

Set up a pre-order gallery where the client will NOT be returning to select images. 

Then attach the download image to their order, to email it is ready. I see this is possible when the image is showing in the gallery and we just update with the larger file. But I have the need for not showing images online but still offer downloads. 

Looks like if the button selected that they will return only for download is checked that they are required to make an account. We would like creating an account to be optional. 
We only have one photo taken so there is no need for them to select anything they just get the one photo sent to them.  

I know it may not work to do the update photo button because there is no photo. However, is it possible to add an attachment button to the email? We would open the order, click email, select the defaut email we wanted and then attach the image. I only see insert image not attach. 

I know/think I am doing more work on my end when they don't have an account, but we have some schools that will not provide emails to us. Therefore making it a hard to password protect and upload images to the gallery after the pre-orders. Just sending the few emails directly currently seems the easiest. Thought maybe I am missing just a click to get what I am looking for. 

There is an option "Customers will return later to select photos for ONLY PRE-ORDERED DOWNLOADS to download those photos." for this very reason. 

Yes, they will have to create an account because that is how it remembers the pre-ordered items. 

Not an option to attach photos to emails coming from Sytist. 

Thank you, that makes sense.