May sound a daft idea but something different needs to happen to make groundsman prepare better pitches.
The ECB need to organise it so that it the game ends on day 4 then the same test teams will play 2x 20/20 games on the last day.
What do they have to loose by playing a couple of T20's instead of a last days play?
Pretty simple - you prepare the wicket we want or you don't get a test gig. The ECB should though offer to compensate them if the county has to issue refunds on day 4/day 5.
Having been fleeced by the ECB at an ODI last year, I know it's never going to happen. They forced through 15 overs in poor weather to make sure the crowd only got a 50% refund.