Actually, I’ve just added this ability to Retrobatch for the next update (1.3.2), which you can grab here: http://flyingmeat.com/download/latest/#retrobatch
Here’s what I wrote in the release notes:
File numbers with leading zeros in the Write node tokens. We’ve not yet added a UI for this, but you can add (and it’s case sensitive) FileNumber04 in the File name: field of the Write node to have the file number of your image written out as part of the name, with a padding of up to 4 zeros. If you’d like to pad that number to 6, you would enter FileNumber06, and so on. Negative values won’t work! And asking for values over 100 is asking for trouble, since MacOS will be angry with you and not allow it.
It’s easy enough to some things like this, it’s always the UI that takes time. So, I’ll get to that when I get a chance- but the basic feature is there, and if you have feedback please let me know!