I am not sure how similar the prohibition of not benefiting from Chametz is to not benefiting from mixtures of meat and milk, so having said that...

I was once given cookies by a non-Jewish friend. The cookies ingredients included milk and - believe it or not - beef fat. I asked an (Orthodox) Rabbi about

• Ba'al Taschit (avoiding wastefulness) and throwing them out

vs

• Benefiting from giving the cookies away

The Rabbi said that I could take them to my workplace (where I am the only Jew) and where it is common to leave snacks for others in the lunchroom, but I had to be sure that no-one knew that I brought it in so that they would not thank me or be grateful to be as that is a form of benefiting from the item.

Which makes me think that you could not buy Chometz for a beggar on Pesach as you would be benefiting from his/her appreciation.

I am not sure how similar the prohibition of not benefiting from Chametz is to not benefiting from mixtures of meat and milk, so having said that...

I was once given cookies by a non-Jewish friend. The cookies ingredients included milk and - believe it or not - beef fat. I asked an (Orthodox) Rabbi about

• Bal Taschit (avoiding wastefulness) and throwing them out

vs

• Benefiting from giving the cookies away

The Rabbi said that I could take them to my workplace (where I am the only Jew) and where it is common to leave snacks for others in the lunchroom, but I had to be sure that no-one knew that I brought it in so that they would not thank me or be grateful to be as that is a form of benefiting from the item.

Which makes me think that you could not buy Chometz for a beggar on Pesach as you would be benefiting from his/her appreciation.