subdomain mapping from a remote site without showing default url

Hello,

I am interested in doing the following domain mapping.
I have an old domain that is currently mapped to a current server with lots of legacy content that can’t be immediately moved (e.g. domain.COM).

I created a wordpress multisite at domain.US.
I have the main site at domain.US and several other sites at site1.domain.US and site2.domain.US.

What I would like to do is map site1.domain.COM to site1.domain.US (without mapping domain.COM to domain.US). I also don’t want the URL to be revealed. E.g. When I go to site1.domain.COM, I don’t want it to redirect to site1.domain.US (since once the migration is done, I want to discard site1.domain.US).

I would potentially also like to do something like directory temp.domain.COM to domain.US.

Now when I try this with DNS entries or ProxyPassReverse I seem to get wordpress errors (wordpress feeling under the weather). If I do it with domain masking it sort of works, but makes the site unusable from a linking perpective. The URL is always clamped to site1.domain.COM and I can’t send links to specific pages since the URL bar never updates.

Suggestions?

Thanks!