I think you may have misunderstood. Pressure from a tumor outside the pituitary will not make you grow larger. A pituitary tumor consisting of active growth-hormone secreting cells will make you grow more.

The pituitary is the hormonal "gland of glands". It releases a few hormones that tells the other hormonal glands when to do their thing and when to stop. One of the hormones it releases is called growth hormone, and it's name explains it's function rather well (it does a handful of other things too, but they are largely irrelevant to this question).

A tumor is a population of cells that are dividing too much and in defiance of the normal restraints placed on cell growth. Basically, they are growing and growing with no regard for other cells' signals telling them to stop. Obviously, these cells are 'broken', but sometimes their DNA is intact enough for them to behave more or less like they used to. If the cells that started dividing uncontrollably were the same kind of cells that make growth hormone (GH), and they haven't gone completely nuts from their mutation, their increased number will mean you have a lot more GH in your body.

If you are young enough to still be able to grow (long bones lose the ability to grow longer during or some time after puberty), you will grow a lot and get a condition known as 'gigantism'. If you are too old to grow but still get a pituitary tumor, you will get a condition known as 'acromegaly'; the few bones left in your body that can still grow will do so. These bones are typically in your chin, but the cartilage in your nose and ears will also grow, leading to the typical acromegaly appearance.

So, for the reasons listed, an implant wouldn't help. Even if it did, past a certain age, it would only help you grow uglier rather than taller.