OK.
Then the best you can do is just use the TLEPropagator
itself, there is no need to convert
it to something else.
So you get the propagator and the ECEF frame as follows:
TLEPropagator propagator = TLEPropagator.selectExtrapolator(tle);
Frame itrf = FramesFactory.getITRF(IERSConventions.IERS_2010, true);
And for any date of your choosing you can call
TimeStampedPVCoordinates pvt = propagator.propagate(date).getPVCoordinates(itrf);
As explained in another thread, if you want to get the position-velocity over a full range, you can use a step handler to pick them up on one go.