Hi Tim,
This is exactly what the base_url config.inc.php parameter is for. For single domain installations you can use it with just:
base_url = "https://yourdomain.whatever"
But if you look further down in the file you’ll see that you can specify domains for specific journal paths like:
base_url[Soremo] = "https://some.other.domain.to.ojs/index.php/Soremo"
and do that for as many individual journals you have.
For Apache, just point all of the domains to the same DocumentRoot and then OJS will sort it out. Domains that are not specified with specific base_url[] directives will load off of the main one in the regular base_url option.
Best,
Jason