There is nothing stopping you from doing systems with no periodicity in QE by just choosing a sufficiently large unit cell. Really though the question is why would you want to when another code would be suited better to it? Also for a system this size, QE may prohibitively expensive depending on your resources.

See also

https://mattermodeling.stackexchange.com/questions/10575/how-to-model-an-isolated-molecule-with-quantum-espresso

Alternatively, you could just use a code that was made for molecular, aperiodic structures. GAMESS offers free site licenses to academic users, but of course commercial tools like Turbomole may do the job faster.