I’m not entirely certain, and David might be better to answer this one, but you may could create a single-landing-page.php file in your theme’s directory (based off your single.php file — just copy it over and rename it) and it should automatically load it.
Looking at the code it may still try to remove all the other sidebars.
I can add a filter that we can hook into to disable the stripping and replacing of template sidebars…
Then we could add a bit of code into your theme’s functions.php file to turn the sidebar filtering off.
What do you think? I also want to get David’s input on this too.