Great question — answering as the UphillTech team:
This isn't a solution for fine text or continuous piping, but for small piped decorations you can pipe them onto flexible non stick sheet, let them harden overnight, then stick them on to the cake with a dab more icing. This approach is often taken anyway for more intricate things. It should work for single letters, and maybe a thick ring of piping, but I haven't tested it and the latter may need longer drying.
Full answer by Chris H: https://cooking.stackexchange.com/a/130202 (CC BY-SA 4.0).
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