Actually, "Num" para style uses a standard auto-numbering:
Use a "DropCaps" char style to fix the drop cap settings:
I've created a "Num" object style (see below) that I've applied to a box I've put in a library.
So, Now, I import it at the beginning of a para (with Num para style).
I cut the anchor marker and then I launch the following regex and replace all.
Done!
As Salah did, the process is very simple and in fact done in one step with a simple regex.
About the block I use with the "Num" object style, It's a empty block with no attribute and nothing in it. Only useful to simulate the drop cap.
Don't forget to prevent manual movement (forgotten setting) to lock the block.