As you may know, in steady DPM tracking you can vary the -number of tries-, which will calculate and display the possible trajectories to be followed by a particle. Each trajectory calculation includes a new stochastic representation of the turbulent contributions to the trajectory. Since these calculations depend on a steady assumption, the force balance acting on a particle is recalculated for every try.
Contrarily, in unsteady DPM tracking the -number of tries- is equal to 1. Here the particle trajectory is evolved step-by-step and depends on the instanteous features of the flow. Hence you cannot display pathlines since the flow doesn't know yet what will occur in the next time steps. You can only display current positions. I believe you will need to reconstruct particle trajectories manually.
What I suggest is to do:
If you have an open system, keep the original injection and let flow to develop normally and establish some few FTT.
Create point injections, keep your particle properties but give a small mass relative to your DPM flow rate. These will act as particle tracers
Define the export settings for these tracers (save local copies of the .his files). These usually contain the particle position, rho, d, mass, T, etc... The higher the saving frequency, the more resolution you'll give to the trajectory
Reconstruct the trajectories based on (x,yz,) positions. Maybe use Matlab