I installed the IBS on my X2 this summer. I just left the starboard overflow hose attached to the thru-hull and cut it just above floor level and attached it to the sac. If I ever want to return it to stock I just need to insert a coupler at the cut point with two clamps and it's back to original. Took me all of 2 minutes.
And ya, you'll only get 300 lbs or so. The cup holders will pop up too -- that's how you know it's full!
2005 X2, Viper Red, MCX, OJ TZ-X5 prop, PPass, rear 750 sacs, KGB, IBS, Bennett Wake Plate, custom wake shaper
(previous) 2001 X5, 1991 TriStar 190