Comment on WordPress AdSense Themes by SEO Dave.
Edit functions.php and find the code for the ad unit you want to float. I’d probably use the one below widget_mytheme_myAdvertsClearBG as it doesn’t have a header saying Adverts and has no background (so just the content AdSense ad unit).
If you use that one change the inline CSS code associated with the div from:
<div style="text-align: center;">
To something like
<div style="position:fixed; left:3px; bottom:15px;">
and see how it looks (I didn’t test it, but should work with a 200 x 200 ad unit).
Should be positioned at the bottom left with a little left padding and bottom padding.
If you change the left and bottom numbers you’ll be able to position it exactly where you want it.
Note this is going to hover over your left menu and won’t be removable. I’d use a smallish ad unit size like a 200 x 200 ad unit. To change to that one edit adsense.php and find
And change the first number in that line to 12 so you have:
$SidebarAd = array(12,2,0,0,2);