You can try double side foam pads.
OR
What I do is use silcone seal. You need to use masking tape to hold the item whilst the silcone sets.
I use this for tray/shelves in the shower & even a soap/shampoo dispenser is held this way.
Grab adhesive will do. Go and have a look round B&Q, they have a cheap brand called Cerafix that make an excellent grab adhesive. Squirt some on the back of the holder and stick it on the wall. You might need to hold it in place with some tape until it's set though.
Of course, those in the know use "Sticks like Sh*t" which is excellent but quite expensive. http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A336149&ts=52840&id=22070
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