Thanks for elaborating on that, @AndZpZ! With interstitials, it might be possible but it is not supported to layer other views on top of the ads.
Is there a reason you are not considering MoPub native ads for this use case? Since you have the freedom to customize the layout and sizes of your native ad assets, you can distribute them to look like a vertical ad, much like an interstitial ad in this case.
Let us know your thoughts.