Add a room to your house where you can plant flowers, similar to the one in land houses. The flower seeds will be purchasable only with $PIXEL and while still alive in your house they will give you some sort of bonus to $PIXEL earning from tasks, for example access to bonus $PIXEL tasks or a slight % boost to the amount you get from all $PIXEL tasks or increased chance of getting $PIXEL tasks or any other type of bonus related to $PIXEL tasks(maybe different type of flowers give different bonuses). Eventually they will wither and die and you will have to repurchase the seeds and replant.

EDIT: Maybe if they give buffs to skill xp gain and energy recovery rate and maybe coin earning will also be a good enough deal for the people to be worth spending $PIXEL on.