Useragent and virtual host

[Lead]

Hi,

I have been using multiple Useragent scripts to crawl other websites, each 
of the scripts are hosted in virtual domains.  My problem is the remote IP 
appearing to the crawled site is the main domain's and not virtual domains'.

I wander if there is other method that I can use such that when a remote 
site is crawled the virtual domain IP appears to them.

Thanks
Lead