Eyeinthesky. Interesting point you made on leaving the gear down in a twin on take-off, until you no longer have enough runway to land ahead on - then retract gear. You need to be careful that you are not painting yourself into a dangerous corner.
By leaving the gear down you are only delaying acceleration to blue line speed and any airborne abort becomes more risky with each passing second.
Also there are no performance figures for most light twins that give you distance needed to get airborne - lose an engine at 100 feet - and abort straight ahead. Therefore it is almost impossible to judge exactly when you have no longer any safe distance to land back on. The situation is exacurbated if it a wet runway and /or night.
Remember that you will be touching down at a relatively high speed with flaps possibly still up, and no anti-skid capability. This all makes for a long roll-out.
There is always going to be a 10-15 second grey area of uncertainty immediately after lift-off which will dictate whether or not you feather and climb out or snap both throttles closed and abort from airborne. Pilot skill and experience plays a great part either way.
Most light twins will reach blue line speed a few seconds after lift-off and providing you have started gear retraction and got the prop feather process underway, then the aircraft should climb single engine if everything is done right. It follows that the best chance of covering your bases is to retract the gear as soon as you have a positive rate of climb after lift off. Do not deliberately delay gear retraction for the reasons given above.