All the Jews in Lakewood...

As an example of the unlimited subdivisions of the mitzvos of the mind, you can train yourself to think that you would like all frum Jews to be blessed.

When you pass by a yeshiva, you can think of asking Hashem to place a blessing upon all the roshei yeshiva, on all the talmidim, on the members of the kollel, all the wives of the kollel, all their children, and on all those who support the kollel. Merely by thinking these thoughts...

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You can build worlds with your mind

...whenever you pass by a place like that, you are performing a very great mitzvah.

Additionally, you are bringing the blessing of Hashem on yourself, as it says, “I will bless those who bless you” (Bereishis 12:3). You are also fulfilling the will of Hashem by giving Him a reason to bless His nation. 

You might be thinking these thoughts about all the Jews in Lakewood, all the Jews in Williamsburg, and so on. You might be thinking that they should all be successful and that they should all have a livelihood. In your mind you are blessing them constantly.

Thus, you are accomplishing tremendous things with your mind,  even though you cannot achieve those good wishes physically. This demonstrates that there are opportunities without end for doing mitzvos with the mind. You can build worlds with your mind. — Ohr Avigdor Hakdama