Probably it is true that the veins of your arms increase with the volume of the blood they have to carry. But, mind you, thats the volume of the blood FLOW. The best way to do this is by working the muscles of your arms. First, with the exercise the arterial blood flow will increase to supply the muscle with oxygen, glucosis and all that stuff. What comes in must go out again - your veins have to transport more blood as well, and will get bigger in diameter (to a degree, not endless

). Second, when contracting your muscles, you put pressure on the deep veins (they run together with the arteries, you cant see them without removing skin/ muscle, and are responsible for the majority of the venous flow) and the capillaries. With that, you pump even more volume of blood in the superficial veins - those we all like to be visible under the skin.
Tying parts of your body off the blood flow is generally no good idea. I too think that you meant impeding the venous backflow like they do when taking bloodsamples - not the hard version with tying off the arterias as well, which is very bad. Ok, the problem with that is that you would forcefully dilate the veins, not make them grow by themselves. In the veins there are valves that prevent the blood from going the wrong way (e.g. back into your hand when you let your arm hang down). If you increase the diameter by force, those valves dont close properly, and the blood starts to pendle (Dunno if that is the right word .. like in going back and forth). That again dilates the vein even more, which again destroys the function of the valves. The result of this you can see pretty often - varicosis, which we really DONT want to see shining through the skin. With all the possible complications like thrombosis and thrombophlebitis and so on.
Im just doing educated guessing here. Im not sure if that would be exactly the same big problem in the arms like in the legs - the arms get far more often at heart level or higher, so the venous flow is better in them anyways, even with insufficient valves. But it sure is a big problem in legs.
You wont see much of veins when you are cold, when you are very excited or in pain (you will have cold sweaty hands then), when you never ever did any work with your hands, and when you dont have much blood volume right that moment for one reason or another. And, of course, when there is a big fat layer above them. Hehe .. but you can still feel them under the fat, like some kind of bicycle tube. So - they are there, waiting for you to cut ...
Just my 5 cents though ...