There's a couple problems here. First, laser warheads, IIRC, don't actually work. At all. I experimented with them once, and they're basically just worse as currently implemented. (It's been a while, though.)
Second, the missiles fire off their sensors as soon as they are launched. If you want to activate near the WP target, you'll need to make them 2-stage, with the sensor in the second stage. (This may not be a bad idea for other reasons, as you can make the second stage much faster than the first.)
I tried something similar a couple times, and even used it in battle once or twice. In that case, they were essentially submarines instead of being fighters, with lots of stealth and sensored missiles. I'd jump them in to a system I was planning to take over before hostilities broke out and have them hide, then fire off their 'torpedoes' to open the JP. But it wasn't really worth the work, because I had to be able to force JPs anyway.
The easy way to keep them from knowing about the launching force is to put your active sensors on specialized vessels that are separated from the missile units. Build those as small as possible, and then scatter half a dozen around the enemy fleet. I'd go with 2-stage missiles, as the current rules make them quite effective. Switch between active platforms to keep the enemy from hunting them down.