This is a very challenging question. As others have mentioned you should ask your Posek to guide you. However, I would like to share some thoughts for you to consider.
First of all it is important to identify what is actually considered the prayer that you would have to focus on to fulfill your minimum requirements of prayer. In terms of your basic prayer obligation the Shmoneh Esreh is the central obligation. The Pesukei Dezimrah are preliminaries that help put you in the proper framework to pray. The Shema is a separate daily Torah obligation to recite those verses. So without utilizing any of the other blessings in Shachrit, the morning service, to fulfill ones obligation, the Shmoneh Esreh is going to be the main way you fulfill your obligation. I can give you more detail if necessary, but my main point is to try to limit what you actually would need to focus on to fulfill the basic obligation.
According to the Rambam in the laws of Prayer Chapter 4, Law 1(as understood by Reb Chaim Soloveitchik, see below) one need only have intent that they are standing before God in prayer for the blessing of the Shemoneh Esreh to fulfill the minimum obligation of Prayer with the exception of the first blessing. With regard to the first blessing of the Shmoneh Esreh one must have concentration of Peirush Hamilim, the concentration on the meaning of the words.
So if you could practice really focusing your attention on the first blessing to focus on the meaning of the words, you would be in good shape. The rest of the prayer, you would just need to try and be aware that you are standing before God. If you find your mind wandering for a moment, just pull back and consider that you are standing before God. By the way, this is a challenge that I believe all people goes through, regardless of ADD or not. It just may be an even bigger challenge for you to address.
Some times ADD can be a result of ones mind moving so fast that the persons mind is thinking about many things and moves faster than what their body or lips can do. Learning to slow things down in your head can help.
My response to you above is not to solve your challenge, however, I am attempting to at least minimize the challenge to a more manageable piece that you may be able to strive for.
Rabbi Chaim Soloveitchik’s Essay on Chapter 4, Halacha 1 Translation
by Jonathan Eskreis-Winkler
It appears correct to say that there are
two types of kavannah in t’fillah. The first type is a kavannah of the
words’ explanation, and its basis is from the law of kavannah. The
second type is a kavannah that he should be m’kavven that he stands in
t’fillah before G-d. As it is explained in his (Maimonides’) words in
the fourth chapter: “What is kavannah? That he should direct his heart
from all thoughts and see himself as if stands before the shechinah
(presence of G-d).” And it seems that this kavannah is not from an
aspect of the actual principle of kavannah, but rather it is just the
definitive act of t’fillah, and if his heart (mind) is not free, and
if he does not see himself as if he is standing before G-d