Implement repeat function for register original insert (help needed)

[sql-koala]

Hi guys,
there is a useful function of register original insert
<c-r><c-o>
that is not clearly documented in Insert.txt, but is demonstrated here for example:
http://vimcasts.org/episodes/pasting-from-insert-mode/ (2:45)

When you repeat such an insert using dot, the current content of the register is inserted. Lets say we have:
"cat" "dog"
On cat, we can do ci"<bs><del>'<c-r><c-o>'<esc> and have 'cat'.
Now, we can repeat that on dog.
I have a working prototype for this but need some help. (from looking at the diff, you will see the basic idea: push down the conversion from InsertCommand.Paste to InsertCommand.Insert text to get it recorded repeatable)
It does not work with a mapping yet (which is what one really wants), so this does not work yet:
nnoremap cs"' ci"<bs><del>'<c-r><c-o>'<esc>

Where do I need to look at the code?