Here is a crude little formula for the seamless playback of an extended sample (e.g. a full acapella track) over multiple patterns.
It uses sliced or offset playback in 15 second chunks (other lengths will work as long too just change what you divide the BPM by).
It involves two steps:
1st: (Beats Per Pattern) = (Beats Per Minute) / 4
2nd: (Lines Per Pattern) = (BPP) x (Lines Per Beat)
Set the lines per pattern to the number calculated and enter the whole sample sequentially at the start of each pattern using offset FX or Slice Markers.
To get the formula to output a whole number bellow 512 for LPP you may have to adjust your BPM and LPB according how you divide the track.
There is probably a less clunky way of achieving this but I figured the above method may as well be posted.