House Rule:
Anything that knocks down an opponent can be used to knock them back instead. The aggressor chooses whether they're being knocked prone or forced to give ground.
On a hit, roll damage as normal; the target must make a knockdown test (also as usual - any relevant bonuses such as Wound Balance apply). Subtract the result of the knockdown test from the damage. For every 5 remaining, the target can be pushed back an additional hex. The pusher may choose to reduce the distance but must move with the target, except for the last space.
For example:
Alaric uses Shield Bash on the wood spirit, who makes a knockdown test and fails by 9. The usual math applies: 0 is the first success, with every additional 5 another success. Therefore, 9 is two successes. Instead of knocking the wood spirit prone, Alaric chooses to push it back two hexes, into the campfire (where it immediately takes fire damage).