I suppose you want this to be your main, you cannot reliably keep a main and keep it illegit unless you can accept the account as expendable.
For starters, cut any current and future illegit activities, you account may already be tagged by TNT for monitoring, you can never know for certain.
If you're desperate, don't do anything fishy for at least 1 month, though TNT can track activity from months before. Ideally, 3 months would be safer, and 6+ months would be safest.
It's good that you're staying under the radar by not going on the boards, keep at that. Also keep neomail convos to a minimum, and trade/auction activity low.
If you haven't already, go over your user lookup and correct anything that looks empty/bland. Eg. filling up your stamp album with 1-50 NP stamps (there is a guide somewhere here about stamp prices, cheapest included), cheap Neodeck cards, a crappy gallery and small shop, for example.
At this point, the only trophies you should aim for are the non-flash ones that don't require scores to be reviewed. If you don't already have them, trophies like Snow Wars, Cheat, Cellblock...and I forgot the rest (there are definitely more).
Google will automatically update a cached page over a few months' time (average ~3 months). There are users here that have been able to request an updated cache for their websites/pages from Google, but the requests are not always granted. Someone else can probably help you better on this topic.
Caching an *updated* page does help, as it makes those dumb nosy PCers harder to pry, you could say it stops them in their tracks, other than their own assumptions. It's only the first step however, as TNT can go beyond that and still look at your activity, as I mentioned at the beginning, from months back.