Okay then, allow me to rephrase my question.

There exists programs such as synner.pl or Xxpoof where one can send spoofed source packets to a target IP address. However, this is only limited to IP addresses. Is there any such way to do the same thing, but to a certain URL, rather than IP?

Say, for example, that example1.com and example2.com share the same IP address, but you only want to spoof an IP packet for example1.com, not example2.com. Would this be at all feasible?