I'd suggest, for innocuous, the classic white plastic-based glue used in
children's artistic homeworks, that one which is soluble in water. There is
the semi-liquid version, and the purer thicker version, much better
quality. The late is widely used in schools hereabout, and it's called
Alkyl. This may be used, adequately thinned with water. In this fashion
it's widely used as a varnish to cover wax-made drawings and the like. If
you have children there around, ask them.
Inigo, from sunny Spain