Include pre-release version, only if stable version does not exists yet

[AlexRadch]

Can I include pre-release version only if stable version does not exists yet?

I develop package that in normal should include stable version of other package. For example 6.*
But now other package does not have stable version. So now I have to include pre-release version 6.*-*

Later when other package will have stable version I will need to change including to 6.* in my package to disable using pre-release versions.

How I can include stable version with optionally included pre-release if stable version does not exist?