It's not the mantra that's accumulated, per se, but one of the prayers. If one is approaching the Mila LaDrup as one's main daily practice, there are instructions for completing the "Nyentsam," or "Approach/Approximation." One recites many of the prayers more times than one would when doing the practice as a group tsok, and the mantra as well, but one of the prayers in particular is what you're accumulating.
There's also no "Jinsek" at the end.....one does a Group Tsok at the conclusion of the Approach recitation.
There are a few places that have the text....I don't know of any on-line except TBRC if you can read Tibetan. It's in Kongtrul's Gyachen KaDzo. KDK sells a pecha format Tibetan/English translation/Phonetic version at www.kdk.org
and you can call or e-mail them to order it, I believe.
You can ask a Kagyu Lama for instruction on how to do the practice, as pretty much every Karma Kagyu Lama has done this practice in retreat, regardless of which monastery they may be affiliated with.