I needed to display a different set of blocks in the right-hand column of one page. To do this I hacked the function COM_siteFooter.
This takes a Boolean parameter $rightblock which indicates whether or not to display the blocks.
I changed this to also support a string, so you can call COM_siteFooter($block_data) and it will display $block_data in place of the usual right hand blocks.
Here's the changes to COM_siteFooter (for v1.3.9 but I doubt if later versions differ much). At about line 1131, change the code after 'if ($rightblock)' as follows:
if( $rightblock )
{
if (is_string($rightblock))
$rblocks = $rightblock;
else
$rblocks = COM_showBlocks( 'right', $topic );
}
if( $rightblock && !empty( $rblocks ))
...
Ideally the $rightblock string should be formatted into blocks, but if your theme allows it you can put any text in there.
One place I see this being useful is the 'related items' panels on story pages, which at the moment don't always behave themselves.