I don't have my own scripts handy, but i'f i remember right all you need is the phonon.SlackBuild and set a CMAKE option "-DPHONON_BUILD_PHONON4QT5=ON". Have a look
here. Just rebuild the phonon package, make sure to rename the final package so you can have both installed.
You can try the SlackBuild from 14.2/-current which builds both (phonon for QT4 and if installed for QT5) but it uses a newer version of phonon which could break things. You can try to use that script anyway, just change the phonon version to what you have installed on 14.1.