Embedding towers of number fields

[switzel]

Hello,

I would like to do this

K.<sqrt2,sqrt5> = NumberField([x^2-2,x^2-5], embedding = [RR(sqrt(2)), RR(sqrt(5))])

but embedding towers of number fields seems not to be implemented (and fails without any warning). Here

https://ask.sagemath.org/question/25312/embeddings-in-numberfieldtower/

it is explained that sage does now about the possible embeddings:

K.embeddings(RR)

but I need to turn one of these into a coercion map. How can I do that?

Best,
Stefan