There is a very easy way. Create a configuration version that explicitly specify the package versions without Snapshotcello.
There is still version 1.6 that is made that way. I tried using it with Versionner but that doesn't work. I load 1.6 but the next time I create a new version it assumes I have 1.8-snapshot loaded which I cannot load afterwards because I refer only to the core but the group isn't there. So even if I would add a manual version I assume it will break the next time you guys add one. Btw. is the metacello mangeling part in Snapshotocello und Versionner not something where forces should be joined? Versionner generates versions that have the individual package versions written in the method.
And I have no glue why snapshotocello is not writing the versions in the version method. My gut feeling is that metacello is complex enough and putting another layer of dynamism in the mix that tries to be clever is probably not the best choice.