The direct approach of putting the frameset code in the wapper would be problematic since you don't want each page to create a new sub-frameset. To get around this you need to put the frameset in a custom template. Create a custom template with this content:
<html>
<head>
<title>{PAGETITLE}</title>
</head>
<frameset frameborder="1" border="1" cols="15%,85%">
<frame src="index.php?custom=yes&TID=leftframe" name="frameleft">
<frame src="index.php" name="frameright">
<noframes>Your browser must support frames to use this site.</noframes>
</frameset>
</html>
<head>
<title>{PAGETITLE}</title>
</head>
<frameset frameborder="1" border="1" cols="15%,85%">
<frame src="index.php?custom=yes&TID=leftframe" name="frameleft">
<frame src="index.php" name="frameright">
<noframes>Your browser must support frames to use this site.</noframes>
</frameset>
</html>
You could link to that directly with wrapper suppression (index.php?custom=yes&TID=yourtemplate&usewrapper=no), but you'll probably want to use the custom template anywhere hack (be sure to change the usewrapper value to 'no' there).
You could avoid having to update any inbound links by moving everything into a subdirectory of where it currently is, then depositing your index.php from the custom template anywhere into the original directory, and having the frameset call the subdirectory's index.php.