Reset Page count, use distinctcount() for page number, or SPROC cursor to reset page numbe

I have a report that will come back as 20 pages.
What the user wants is on the beginning of another unique ID, which causes a new page to be started, to have the page count restart to 1.
So, if I have 3 UniqueIDs for all 20 pages, and the first, IDAA, is 10 pages long, the second, IDBB, is 4 pages long, and the third, IDCC, is 6 pages long, then the page numbering would be as:
1-10 for IDAA
1-4 for IDBB
1-6 for IDCC
I've been told to set a cursor in a SP that determines what page I'm on and then passses this to the result set as a column. This is then set in a group to control page breaks. How could I do this? I'm not very familiar with SPROC cursors.
I know how to do this scenario in Crystal Reports, but am trying to figure it out here with either a page count formula, or some type of distinct count().
Thanks!

This is what I've tried so far, but it resets on every page.
So, each page is 1 even if the Unique ID spans 2-3 pages.
I only need it to reset on a new field grouping of the list object.

Here's the VB code for the report:

Shared offset As Integer

Public Function GetPN(reset As Boolean, pagenumber As Integer) As Integer
If reset
offset = pagenumber - 1
End If
Return pagenumber - offset
End Function

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In the header, I have a textbox named "tag"

In the footer, I've got the following expression:
="Unique ID Page: " & Code.GetPN(Not(ReportItems!tag.Value Is Nothing),Globals!PageNumber)

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Blank

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My fault...I had the textbox "tag" in the page header and not in the list object itself.

It works!

Thanks!