For the benefit of anyone stumbling on this topic in the future:
Simply appending /defaults to the commandline in the shortcut will fail. It will cause the shortcut to change behavior from bringing up the confirmation dialog, uploading (after user input) and exiting.. to simply opening the program, not touching the file.

Instead, place the /defaults switch before the /uploadifany switch. The latter actually takes a parameter (just like /upload) and so you have to act accordingly.

It's odd that the program creates the shortcut with the /uploadifany switch when there isn't any documentation on it anywhere, as far as I can tell - even googling the entire internet only turns up 3 irrelevant results - two in German, one in Japanese. AFAICT, /uploadifany is simply a version of /upload that does not return an error if it's used without a file list present.

Edit the icon and add /defaults parameter.

Please make it possible to suppress the 'transfer' confirmation dialog box when using the "drop files on winscp's icon" option. Even with confirmations suppressed (everything unchecked in the environment->confirmations preferences section) this still pops up. It's downright silly to have an icon to a specific remote directory, drag a single file to it, and then be asked where I want to put what I'm uploading.