What I want is to commit a package or group of packages to both repositories at once, with the same version number if possible, so one repo can be mirror of the other.
Is it possible using Gofer?
Gofer can take more than one repository per operation. Try:
fileTreeRepoDirectory := FileDirectory on: '/path/to/repository/'.
Gofer it
squeaksource: repoName; "e.g. 'Seaside'"
repository: (MCFileTreeRepository new directory: fileTreeRepoDirectory);
package: packageName;
commit: messageString.