Problem about hosting and domains

Hello.

Recently I ran into a small problem: there are several domains registered for a project that need to be redirected to the main project domain (let's call it B). But domain B itself is an additional domain on the hosting, where the main one is A. In total, hosting allows 4 additional domains that refer to their own directories. Of these, 3 were used. In addition, there is the possibility of parking an unlimited number of domains, but they park on the main domain A.

Domain 8 needs to redirect 8 domains (and it’s better to put them in a mirror), but there are no free additional domains on the hosting. Change the primary domain is also impossible.
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What options do I see:
1. Purchase support for additional domains and link them to the directory
2. Buy a separate hosting for the project
3. Park to project root A, and make a script that redirects by domain name as an index

Varian number 3 I like most because of its free. But the feeling that this option is not optimal and there are still some solutions does not leave me. Yes, and to fix the project A because of B is somehow non-systemic. If you have any suggestions - please.