The reasons you have said that using an inverted index isn't practical is that

a) you need to support searching for phrases

Matching phrases against an index is a case of splitting the phrase into its constituant words, and then intersecting the sets of record numbers that are returned from the index. (see Re: Idea for XPath implementation for slightly better explaination of this).

And, or & not are just extensions of the set manipulations.

b) you need to support partial matches.

Partial matches are a bit more complex, but davorgs Tie::Hash::Regex as the basic for your inverted index,

or use grep /partial.*., keys %index; (which what is used under the covers).

This would probably involve using doing some manipulation of the input query to convert partial matches to regex notation (eg. bio* => bio[^\s]*), unless your users are comfortable using regex notation.

Just a thought in case you haven't already considered this.