MacPorts custom installation prefix and precompiled binaries

[Jordan Ellis Coppard via macports-dev]

Hello,

I read in the docs that if MacPorts is installed anywhere other than 
/opt/local that precompiled binaries can not be used. I cannot find this 
statement again so I am unsure if there was additional explanation for 
why; so.. why?

I'd like to be able to use MacPorts at a custom prefix but still also 
use precompiled binaries sometimes (particularly those using Rust) due 
to the incredibly long compilation times.


/Jordan