This abuse is possible b/c of the high weightings on individual governance proposal rewards. Setting a fixed % of voter rewards attributable to governance proposals on a daily basis would solve this.
Something like, you receive X% of total potential voter rewards per day based on your governance participation. The mechanism for doing this is outlined in Proposal to fix governance proposal rewards at 75% on a daily basis.
I think this combined with your idea of rewards without redistribution might be the solution.