[Feature Request] Callback/Pre-upload script

I was wondering if it'd be possible to have a method get called before it starts an upload, this method would retrieve a Signed URL for uploading to a service like Google Cloud Storage or Amazon S3.

In our application (currently written in Ionic/Corvdova, now being ported to flutter) a user may take or select up to 250 photo's at a time, and possibly video file(s) in the future, on top of that we're looking to add Offline Support so that users can select their photo's while they're offline, and once they have network access (or even restrict uploads to WIFI), the uploads would start, however each file needs a unique signed URL in order to upload.

I have done a very rough lookover on this plugin and it looks like it's fairly close but I'm not sure if it's possible to have the plugin run a function before to retrieve the signed url.