EDIT Now I do understand why it's not doable with fixed clamps. So I have closed the poll. It's doable only if you use flying clamps. Since you have a starting knot at the beginning of the process, it's like using one clamp for each side of the mains. You don't use 4 clamps for the mains to make sure the tension is good or for safety purpose too. For the mains, for sure you need 2 clamps. (even 3 for the start). But for the crosses, it's just more for safety purpose and because you are used to use the two flying clamps for practical reason and habit.
I am sorry but that's just crazy talk... Saying that having two clamps is a disadvantage is like saying having two hands is a disadvantage. In addition to safety and extra support to reduce setback and tension loss, two clamps also help to speed things up. It is much faster just to move the clamp 2 strings up than side to side and also if you have two clamps the second one can be loosened safely before fully achieving the tension so that you clamp it exactly when the right tension has been pulled. As @emjay pointed out consistency is the most important factor. I don't believe that your OP idea would improve final result, as any manipulations that you do to extra stretch the string will lead to very bad result since there is no way you can recover the tension exactly every time and the more things you try to do the less consistent result you will get. The best is to do exactly the same thing every single time. Same way pulling the string, same way clamping. Making sure the time is the same every single pull since the time affects how much string is stretched during the tensioning. Best not to do anything to combat setback if your clamps have it, just make sure you have it the same every time and if the final tension is too low, add as much tension as needed next time... By the way there is absolutely no need for four clamps on mains... There is no weaving and therefore nothing much can happen and even if you do loosen a clamp - it will take only a few mins to redo them. Unlike crosses where you will have to redo the whole thing and possibly even throw away the string...
