How to update Embedding vector in keras with custom operator

Suppose I have two features f1, f2 with corresponding embedding vector e1,e2 built by keras Embeding layer, how could I update each vector with some custom operation instead of only using gradient?
For example , I would like to update e1 as follows:
e1 = 0.9 * (e1 + learning_rate * d e1) + 0.1 * e2