OP - what kind of bugs did you use?
After a year, you're probably not going to get any more acidity out of lactobacillus, even after adding the fruit. If you used a culture w/ pediococcus, it may kick up in the next few months.
If you choose to wait on the pedio (which I recommend), hold off on adding fruit or transferring. Pedio likes an oxygen-free environment, so disturbing the beer may impede pedio's acid production.
1. Pitch a store-bought culture of pedio. Make sure to minimize O2 pickup: handling, transfers, etc. Treat it just like you would a hoppy Double IPA. Wait another 6-8 months (at least) before sampling again. This is a good idea even if pedio was in your initial pitch.
2. Use acidic fruit. Tart cherries, rhubarb, wine grapes, cranberries, or raspberries. Rhubarb complements other fruits nicely and adds acidity.
3. Adjust acidity w/ lactic acid. If the acid level is fairly close to what you want, adjusting w/ lactic acid is a great option. I like to do it in the keg, so I can pour a carbonated pint, adjust dropwise, then scale up.
4. Add fruit juice fermented w/ lactobacillus. A new pitch of lacto may not thrive in the existing beer, but you could pitch it into some fruit juice to create acid before adding the juice to the beer. I've never tried it, but I've made lacto starters w/ fruit juice, and the decanted wort is usually quite tart. Its also similar to how I make Berlinerweiss (with a small portion of wort instead of the juice).
Let me know how you go about it, especially if you try the last option - I'd love to hear the results!