R' Moshe Yehuda Gluck asked:
> Isn't that a problem, re: Lifnei Iver because of their
> not making Berachos?

R' Joel Rich responded:
> I don't have the cite but I'm pretty sure R' SZA paskened
> this was not a problem in a kiruv situation.

Rabbi Doniel Neustadt's article at 
http://www.torah.org/advanced/weekly-halacha/5761/reeh.html is 
entirely on this topic. One part of it is:

> The poskim suggest several leniencies that alleviate the
> severity of the prohibition of serving food to a person
> who will not recite a blessing over it. In the following
> cases it would be permissible: 
> ...
> 7. If, by offering him food, there is a better chance of
> bringing a non-observant Jew closer to religous
> observance(10). 
> ...
> (10) Harav S.Z. Auerbach (quoted in V'zos ha-Berachah,
> 4th edition, pg. 154).

Akiva Miller