Do you still see ads even if your phone is offline?
Most ads require internet access.  If you remove the internet access, then it shouldn't load the ads (unless they are somehow cached?).

If he really, really, really wants to get rid of ads all together, you can install the AdFree app on rooted phones.  It will remove ads from the browser, from apps, etc.  Anything that is in its blacklist will refuse to load.

However, developers do try to make a living and often provide their apps for free at the cost of a little advertising.  You may also want to try and explain this to him and if he really likes the app he can support the developer further by purchasing the full (ad free) version.  No money, no developers.