I’m afraid “special” ties - cross-voice ties, or ties from grace notes to normal notes - don’t appear in condensed music. Internally they aren’t represented in the same way as normal ties.
If you give your grace note a laissez vibrer tie and make the grace note disappear by hiding its notehead, stem and ledger line, you can fake a tie from the previous flow which will not disappear when you turn on condensing:
If Ben were to reduce the gap between flows during playback to zero, suppress playback of the tied-to note at the beginning of a flow, and use the playback end offset of the tied-from note at the end of the previous flow to increase the played duration of the tied-from note to include the duration of the tied-to note, he could obtain correct playback of a note tied between flows.