How can I run command line software with Rosetta 1?

At the request of some PPC users, I'm trying to create a PPC-compatible installer package of some open source software. Naturally, this requires compiling a PPC binary. I have a Leopard Virtual Machine set up on my Intel Mac, but I don't have access to any actual PPC hardware. MacPorts does not offer any C++11 compilers which can cross-compile PPC binaries on Intel, but I'd thought I'd be able to work around this by running the whole of MacPorts under Rosetta. With Rosetta 2, this would be easy —I'd just set the Terminal app to "Open using Rosetta", and everything the Terminal runs would *also* use Rosetta. This was a commonly recommended way to run Homebrew on M1 Macs, before Homebrew finally added native Apple Silicon support a few weeks ago. Unfortunately, Rosetta 1 does not appear to be this intelligent. I can set the Terminal app to "Open using Rosetta," but this causes only the literal Terminal app to use Rosetta. Bash, MacPorts, etc are still running as Intel processes, according to Activity Monitor. Is there an alternate way to run command line programs—and preferably all of MacPorts—under Rosetta?