We have a set of canonical functions that can be used in EntitySQL to operate with spatial types, which include instance construction from well-known text. For instance, this is valid EntitySQL for constructing a point:
GeometryFromText('POINT (43 -73)')
The full set of spatial canonical functions is declared in the SpatialEdmFunctions class, but this class is used for creating DbExpression trees programmatically, so the reference documentation available for this class is not in the most appropriate form for EntitySQL usage. I will follow up with our documentation team to see if there is a better resource available or if we need to add these to the EntitySQL documentation.