How to prevent candidate from moving to Core HR

Summary

We need to avoid that the external candidate turns into a worker

Content

Hello,

Our HCM is a slave system. This means that all employees are integrated into the Core HR from other systems. We are trying to set up the Job Offers. 
However, we need to avoid that the external candidate turns into a worker.
Does anyone know how to "hiring" a candidate, without move him to HR Phase or without to convert him as pending worker, but maintaining the Job Offer fase? 

Many thanks,
Emanuela