Refining subject navigation/search with eea Faceted Navigation

I want to access documents with the following tag condition (using eea faceted navigation)

Subject1 and (Subject2 or Subject3)

I ended up using TAL widget in conjunction with Debug widget so as to construct a portal_catalog query that will resolve the condition above... with no success

i've only got one of the following querying types :

{ 'operator':'or',
'query':['...Subjects..']
}

{ 'operator':'and',
'query':['..Subjects...']
}

does anyone know how to construct a portal_catalog query that can give me the results for

"Subject1 and (Subject2 or Subject3)"

Thank you