Thank you both for your replies. 

This is a part of my PhD project and I am actually planning on going with DEFINE_DPM_SPRAY_COLLIDE. In fact I already started working on it. But as @rwoolhou correctly noted that the easiest solution implemented in Fluent of looping only over one cell, where the tp is currently residing, is not necessarily the best solution, my idea was to find an alternative to this first. However, as you both may be able to appreciate how challenging even only this small part is.