I am also interested by the answer.

@webgames, the "is it okay?" question would be a question for Adsense support.

My question is how exactly would this work?

Is it even possible?

The back up ads, is simply the URL of a page, which is displayed in an iFrame, so yes it's possible to put on this page the matched content code. And this will work However, it's unclear, what's the rules to display the matched content. Since it's made to promote your own content, there shouldn't be restriction on how you use it. However, since it's possible to "monetize" it, it's possible there are a minimum of requirements. For example, it's forbidden to display adsense in an "empty page" (no content), and inside an iframe , the backup ads page is an empty page which will be displayed in an iframe. So that's why the question of webgames is pertinent. And I am also wondering if this is allowed or not.

Is it possible if you have Match Content enable like Dimitri explain above. Thanks Dimitri ...

This still makes no sense to me.

If you add the matched content to the back-up url will it not appear at the bottom of the I-frame? Will it be legible? Why not simply add the code to all the pages then it appears whether the ads are filled or not.

As for monetizing, again something seems off. If Adsense is suppressing ads because there is too much inventory to meet demand how is adding extra ad-units (matched content) going to help. Those will most likely not be filled either or filled with the crap your trying to block with the ad balancer.

I think webgames wants to avoid a blank space, when ads are not filled.

And as for the matched content ad inventory, I am not sure it's the same inventory as for the adsense "normal" blocs. But I might be wrong.

@NickMNS - When i enable to certain % on "Ad Balance" there are a lots of blank space. If i use the match content with ad enable, i may make some money and fill up the space. I'm not sure if Adsense allow this or not.

i may make some money and fill up the space.

Your ads are blank because there is not enough demand to meet the supply. If you add supply you are simply exacerbating the situation.Maybe an will appear in the matched content unit, but then you will have one less ad appearing in its regular slot.

Lets assume that Dimitri is right, and the inventory is from a different pool, and not impacted by the ad-balance. I still think that back-filling with matched content would be sub-optimal. If there is sufficient inventory in the matched content pool, why would you limit that content to pages where ad are not shown. Wouldn't it be preferable to take full advantage of that inventory and display it on every page? Should it not perform better then on high demand pages?

Using affiliate link as a backfill makes sense. There is no guarantee that an affiliate link will be well matched to the user, so CTR overall should be less then with optimized ads. So show as many high earning ads as you can, once the demand pool has been consumed, then show the affiliate links. The low CTR with a relatively high payout from the affiliate is better than high CTR with little to no payout (low cpc ads).

If you want to make "some" money on blank space, then increase your Ad Balance %. Matched content won't help you anyway, and it's not good for user experience either, if visitor seeing the same matched content over and over again.

You're not allowed to place AdSense ads in an iframe, which is essentially what happens with backup ads. However, since you're not looking to manipulate anything, contact AdSense support; they may still give you authorization.