The short answer is no.
The long term answer is file an RFE to request this be added in the future, though I wouldn’t expect it anytime soon. How to ask for IBM product help: PMRs, RFEs, and more
The long answer is that you could technically change the hosts file on the root server to cause it to look at an internal web server to your organization instead of Microsoft’s download site. Then you would have to populate this web server with all of the microsoft downloads you wish to use in the exact path that they are normally located on Microsoft’s site and in the prefetch commands of the BigFix patches. It might be possible to automate this somehow with the REST API, but it wouldn’t be easy.
Ideally you would use a proxy server to allow the BigFix root server to talk to Microsoft’s site and Microsoft’s site only. This does remove some of the AirGap, but I think in a reasonable and controlled way that doesn’t open up any potential attacks on the root server.