Summary

Y-axis of the Prusa i2 (or any other compatible version) is normally limited to the dimensions of the printer. I built my Prusa i2 with an over-mount Y-axis smooth rods allowing the print bed to roll over and above the frame. This requires 1 extra long Y-axis smooth rod to mount the end-stop. Bend the long smooth rod or cut it as required.

Instructions

For an extra long Y axis (~330mm on my Prusa i2)

Over mount the Y-axis smooth rods.
Decrease the distance between the belt mount points on the Y-axis. They should be closer to each other on the Y-axis to allow additional traversal length above the over-hang.
Decrease the distance between the linear bearings for the added traversal length. Bringing the linear bearings too close to each other may increase vibration on your print bed requiring other forms of bed-stabilization. Just find the optimal distance that is appropriate for your printer.
Use one extra long Y axis smooth rod to mount the end-stop as shown in pic. Trim it to size and cap it, or just bend it as needed. Ensure that bending the smooth rod only happens at 1 location, else the bed traversal will be compromised.
Enjoy longer (y-axis) than earlier prints on your 3D printer.

Extra long Y-axis on your 3D printer