There is one house in Las Vegas that uses pins that have a flat magnetic tip on the top of them, and the pinsetters use those to set the pins. The manufacturer is Mendes. And with their scoring system, you can spot whatever pins you want at any time, from full rack, to having to re-spot a pin from having fallen over after the pinsetter hit it. That would be what you're looking for.
Now, having that said, if you are a "pin aimer" and can't have any middle pins up, that speaks more about your inability to control your ball than anything. I've said this here before, and this is a prime example of why we did it in my collegiate days, so I'll say it again.
One night during our team's practice, our coach had us go through 32 out of a 40-lane house, starting on lane 1, and take the 7-pin and the 10-pin ONLY off the rack. If you got only those two, you went to the next lane and did it again. Wash/Rinse/Repeat until you got those on lane 32. After that, you could go home. For example, if you were able to get the 7-pin, but took out the 6-pin (and whatever pin it deflected into) and the 10-pin, you stayed on that lane and tried again. Most of the team took 90 minutes to two hours to finish, while the first one done finished in 45 minutes; it was a lady, at that.
Doing this not only helps with your accuracy to take out corner pins, but as a byproduct, you may have a better chance of picking up a 6-7-10 or 4-7-10 because of how you can miss to the right of the 4 or 6-pin and still keep the ball on the lane. By your own admission, if middle pins are bothering you so badly that you can't take out a corner pin, you depend way too much on room, your accuracy is way down, and your two-handed delivery is severely hurting your spare game.
Everyone here has given you advice on what you need to do, and they all have been the same. To go further, I'd suggest dropping a 2-handed delivery for your spares, because accuracy counts for those, and as mentioned by myself and others, your accuracy on spares is highly lacking.
BL.
