Sequential numbering in remain

Hello,

I would like to rename photos in a directory using the following format: DayMonthSequentialNumber. For example: 25May01, 25May02, 26May01, 26May02, 26May03, 27May01. Unfortunately, sequential numbering in the Opus remain dialog increments all files in the directory. In my example, I get 25May01, 25May02, 26May03 etc. The best what I could find is using “Automatically rename if new file name exists” option. But this option does not add number for a single file and cannot be formatted. Therefore I should do the second remain with quite complex regular expression that is tedious. Does anybody know the method to do this in simple way? Or should I use the heavy artillery such a scripting language for this task?
Thank you, Toller