$base_url in settings.php

i run a site on drupal 7.
for security reasons it would be good to set the base url, but i’m wondering what to do, since i am running the same install on different domains, it is not a multisite because the different domains all do point to the same install // database.
when i set the $base_url to domain1.com all other domains will change to that one too, while surfing the site, which is something i do not want ..

so is there any way in settings.php to set multiple $base_urls ?

all help very much appreciated!

Drupal version: 


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