For just a moment let's look at what we do know.
1. The testicles hang down in the scrotum so that a cooler temperature can be maintained. Average body temperature for any kind of sustained period causes damage.
2. Surgically several MD's have used a technique which implanted an "overlay" enlarging the testicle by placing basically a sheath over the top of it. The problems with this surgery have been numerous. The scrotal area is an easy one to have infections. These can also shift and cut off full blood circulation to the testicles in which case testicular damage can take place before a second surgeon could repair the shift. Also not good.
3. Silicone injection has had numerous problems and these often do not show up for a protracted time after they are done. If encapsulation issues start to rear their head the damage may not show up for several years. In addition, the silicone works as an isulator and raises the temperature. Bad enough and anything other than short term saline can cause the sources of testosterone and other necessary things for sex to be nothing but a memory.
4. I have heard of enlargment from Tonkat Ali. There are many grades of Tongkat Ali and it appears that those which are effective cost well over $1000 for a cycle. Again, those who have had the grand to spend have consistently reported more than a few good things from it's use.
5. Vacuum pumping of testicles in a manner of speaking as a general rule does not actually enlarge the testicles, but, it may cause them to hang lower and stretch the scrotum over time. This may give the impression of things changing. For the most part pumping that includes testicles draws lymphatic fluid into the scrotum and the pumper gets a temporary effect.
6. Medically, the main stimulator of testicles is Human Chorionic Gonadotropin when used directly. The testicles are stimulated by this drug to go into warp drive and to start producing everything they can.
7. HGC can create a refractory period and as a rule it is cycled. It is not horrifically expensive, but, most MD's would not prescribe it on an average to anyone for cosmetic reasons.
a. I have recently discovered that there seems to be a circumstance where it can be prescribed for this purpose. HIV patients who have been on long term testosterone therapy and show testicular atrophy can be prescribed HCG therapy AND it appears that under this condition most State and many insurance companies WILL pay for it. This is a surprise to me and I only learned of this one about 6 months ago.
b. If you are given supplemental testosterone therapy for any reason you must also be given HCG if the testosterone ester being used is NOT DHT. The body does not recognized DHT for some reason and will not down regulate unless the dosages are elephant sized.
c. If you are one who qualifies for testosterone replacement try every way to make certain that the MD does not short-cut the whole thing and make certain that what you are prescribed IS DHT if at all possible. The Andro-Gel cream IS available in a DHT verison.
There is no way at present to guarantee a safe manner to enlarge testicles. There are some drugs and one herbal that might be effective, but these can have other negative effects if used incorrectly.
I would focus the efforts personally on enlarging the penis. If the penis is large enough after all, who's going to look at the testicles?
Good Luck. . . .