I understand where you're going with this but I don't think it's (currently) do-able. There's no way to programatically determine style attributes. PROC REPORT doesn't know anything about panels or RTF, it just knows about columns. RTF doesn't know how many panels will fit on a page because it doesn't know the page's length.
However, for what it's worth, the new "measured RTF" support in SAS 9.2 has an option that lets you specify the maximum number of panels on a page (because measured RTF does know about page lengths) so you could do exactly what you're asking for. I realize that doesn't help you much today. Sorry.
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