1. Try rearview mirror glue from Halfords etc, the type that has a little phial of hydroflouric acid to etch the areas you are going to glue before you actually glue it.
2. If that doesn't work use the 5 minute araldite- the optically clear one is best (I think) so you won't notice any glue so much once it has dried.
3. If that is no good just go for the 24 hr araldite. It's a lot stronger than the 5 min variety.
In all cases cleaning with solvent and not touching anything afterwards, and clamping in position while drying, are all essential.