How do I lay out the special offers page when most offers only apply to one product?

I am building an ecommerce web site, and am trying to find a way to present the special offers. Products on special offer are grouped, so the offer applies to all products in that group. For example, there might be an offer on Jimbo's chocolate, where if you buy any of their three products, you get a second one free. That offer has three products in the group. By contrast, Rice Krispies may be on special offer, but the offer only applies to that one product alone.

At the moment, the special offers page looks something like this (irrelevant parts removed for clarity)...

This isn't great, mainly because there is a lot of white space in groups where there is only one product (the majority of them).

I thought about making the group box only as wide as the number of products, but that got very messy, as the last offer in the row often had the wrong number of products to fit on the row, so dropped onto the next row, leaving the previous one short. This gave a very ragged look to the right hand side of the page.

Anyone any suggestions how to group the offers neatly, but without wasting so much space?

Thanks