Does sage support transcendental base rings?

[Michel]

Hi,

In need to do some Grobner basis computations in rings of the form
QQ(a,b,...)[x,y,z,....].

It is possible to define such rings in Singular. However I am afraid
that if I define them in
sage in the usual iterative way

R=QQ['a','b','c']
K=FractionField(R)
S=K['x','y','z']

I will not get the Singular optimized version. Is this true? Is there
syntax so that one uses the Singular version?

Regards,
Michel