Customizing a plugin

I need to customize this plugin: https://www.ads-software.com/plugins/frontier-post/
I want to change the image uploading part. The uploading should work like in this plugin: https://perishablepress.com/demos/user-submitted-posts/

So I want it to be simple one click upload and not use WordPress media gallery.

Can anybody help me with that? I have contacted the plugin author, but he is not doing customizations.