In the interim, employee incentives (ego, bonuses) to being listed as an "inventor" while BigCompany remains the "assignee" could be ameliorated with a "Software Patent Hall of Shame" (SPHS), which would list software engineers complicit in software patents.
This would disincentivize software engineers from stealing ideas, from allowing their work to be patented, or from signing agreements which would force them to do so, since doing so would undermine their prospects with future employers, who believe in free and open software and unencumbered computer science research.