You could just rub a sliced garlic clove over the cucumber. Someone suggested dipping plec wafers in tank water, rolling in garlic powder then freezing. Good luck getting them to eat.
May be worth trying courgette or butternut squash rather than cucumber - mine have always rejected the latter outright. Have they suddenly stopped eaten? Have they been moved recently or anything added to the tank? What are your water stats like?
Thanks for all the info! I ended up buying a garlic like gel that you squeeze from a tube. All stores stated that have no hispanic customer base so they don't carry garlic extract. Doesn't make sense. Anyway I added both cucumber and courgette last night. Seems the rubber lip has some of the courgette and ate only the garlic on the cucumber... My panaque did come out when the garlic was added but no eating that was witnessed. I will keep chaning them every 36 hours and hope to see some fat bellies within 3-4 days....