Erm...improvise

Get two long slim sticks or rod which can also be made of either wood or bamboo or even stainless steel. Slice out one portion of the cucumber skin...use it like a pleco chum...attracts them faster this way. Stick the stick through the bottom side of the cuke and in another position...so when seen from top it should look like an X.(/ being the cuke and \ being the stick) After that get a rock...heavy enough that ur pleco wont push around and let it sit on the stick. Make sure its snug...because plecos can be really rough when it comes to food...and if that happens they wont touch ur floating cuke...unless they are darn desperate...like mine...hahaha they actually come to the surface as the cuke and stick got dislodged from the rock.

I have erm..about 20 plecos in that tank...most are still about 5-6 cm sizes and one cuke is like erm...army ration...its never enough.

Be warned though that cukes will cloud ur water...always give them cukes when u are about to perform a water change.