Yes, you can. To do it, you need to switch on the "show banners only" option. You can do it this way: Campaign page -> Traffic sources -> Selection criteria:
And press a blue pencil here:
There you can set on "show banners only" option:
But you should add as many banner sizes as possible before doing this. Mind, please, the most popular sizes are as follows:
You need at least 468*60, 300*250 and 728*90 sizes as they cover ~67% of traffic.
Mind please that if you have a banner and a text ad for one ad unit size, banner is shown by default. If you switch on "show banners only" option, all the adaptive size ad units become unavailable for you, no matter if they suit your banner size; so the amount of traffic you receive becomes less. So if you have all or nearly all banner sizes you probably don't need the "show banners only" option.
After you set on the option, please, check your estimated daily performance at your Budget page: the quantity of traffic will reduce and the campaign might become inefficient. Take care!