One thing you can try is blocking the front air intake grill or at least part of it. Use some of the cylindrical foam A/C insulation found at any hardware store, for example. This should allow the engine to retain more heat and get to EV mode more quickly. Will it be enough on a 7 mile trip? That I don't know but it will be inexpensive to find out.

Alden Bowles
2005 Toyota Prius II HSD