I made up a couple of feats to allow sneak attacking with a crossbow out to the first range increment:
Crossbow Expert [General, Fighter]
You are exceptionally skilled at the use of crossbows.
Prerequisites: Base attack bonus +6, Point-Blank Shot, Weapon Focus (crossbow), proficient with crossbow.
Benefit: When using a crossbow, your damage die increases one step, according to the rules for upsizing weapons in the DMG and MM (1d8 or 1d10 becomes 2d6). You can also apply double your Int bonus (if any) to negate attack penalties due to range. This does not result in an actual bonus to attack; if the doubled Int bonus is greater than the range penalty, the excess is discarded.
Crossbow Master [General]
A crossbow is truly lethal in your hands.
Prerequisites: Base attack bonus +8, Crossbow Expert, Point-Blank Shot, Precise Shot, Weapon Focus (crossbow), proficient with crossbow, sneak attack class ability.
Benefit: When making an aimed shot with a crossbow (see the Improved Aimed Shot feat, below), you can make sneak attacks out to your weapon’s first range increment. You must still meet the other requirements for a sneak attack.
Normal: A character without this feat can only make ranged sneak attacks within 30 feet.