If the rake task call only thirdparty gems, then you can call plain ```rake sometask```
If you put 
```Requires: rubygem(foo)```
in spec.
And we need to distribute such gem beside its SC version. But that is usually not problem.
But if the task use our own code (which this one seems to do), then you either have to distribute code for ruby1.8 and SC ruby 1.9 (which we dont do) or you have to call this task from SC environment.
Probably best option is to create /usr/bin/ruby193-rake wrapper (ruby193-ruby already provides similar wrapper for ruby itself) and do something like this in spec file:
```#replace shebangs for SCL
%if %{?scl:1}%{!?scl:0}
    sed -ri '1sX(rake |/usr/bin/rakeX/usr/bin/ruby193-rakeX' katello-configure/upgrade-scripts/0750_republish_repos.sh
%endif
```