Is there a way to instruct visual studio to give each instance of a user
control a unique attribute value, by specifying a pattern for an incremental
index? Similar to how visual studio automatically determines a unique ID

For example, if my control has an attribute panelnumber, as in:

<my:panel panelnumber="pan1" runat="server" id="panel1" />

I want to establish a pattern placeholder, eg "pan##", whereby VS.NET will
replace the ## with a unique number: pan1, pan2, pan3, etc.