Our game has 2 gift-suppressing effects. One we started with, and is a curiosity of the interaction of our regio and our aegis: the effects of the gift are not felt within the aegis. This was part of the premise of our covenant, to permit certain interactions with the university of cambridge. Not helpful for your campaign however.
The second is from Bath - specifically an underground set of baths directly fed from the great engine of Bladud. I gave the baths there three effects: suppress the gift, suppress lycanthropy and cure disease. This has been discovered by the party and used as an insight for further research.
We agree that "suppressing" the gift must weaken it, so much so that one character who had dwelt too long at our covenant had their gift suppressed entirely. Therefore, the insight our criamon with focus "seeing beyond the mundane" had (and after some ordeals for our degifted character) was to recreate the great fermenting engine, but in reverse: baths which when bathed in make the gift more blatant. After adventures to secure the mythic salts...
Our magi created this new set of baths, which allowed our previously degifted character to rediscover his gifts. To take advantage of the gift suppression effect, one must balance it with the gift worsening effect of the new set of baths to avoid losing ones gift.
However, we also wanted a systematic explanation of King Bladud's engines and their magic, so we can recreate new baths. This line of discovery will be through a mystery cult dedicated to Aqua Sulis.
Basically the core things we have decided upon about the engines, is that the 7 mythic salts determine the effects of an engine, which confers its powers to the waters it ferments. The 7 mythic salts correspond to the 7 astrological planets, of which 3 are primary (and hence determine the effect), with the topic of the effect (e.g. Health/Disease for Sun, The Gift for Mercury, Lycanthropy for Moon) and the expression (suppress, embolden, not sure yet) determined by the other 4, the order the salts are added, the vessels etc.
So when they "recreated" the engine, the primary salts and the topics were unchanged, but the expressions were because they didnt truly understand the underlying theory. Now the characters need to research if they want an analytical understanding of Bladud engines, and to perhaps integrate them into Hermetic magic. The effects of Bladud Engines should always be based around virtues/flaws imo.
This is just what we did, but it was the source of many stories both in and out of Bath (lots of fun things you can do with finding the salts), allows introduction of a mystery cult and can lead to a whole new facet of magic based around the conference/suppression of virtues/flaws imbued into water based on the planets (from the mysteries). So perhaps any of this could be a fun addition?
Oh final thought, if you have gentle gifted character and you overcome the gift, I think you should allow the character to pick new virtues (either 2 if the gift is partially suppressed, or 3 if fully), just as I feel you should allow characters with good [characteristic] to pick a new virtue if your magi develop spells to increase their characteristics. New virtues are ideally developed as part of the story.