Here's what I do in Blood and Fists- first there are two new uses for the concentration skill.
Concentration (Con)
New Use- Meditation (this use of the concentration skill may not be used untrained): Characters trained in concentration may make a skill check (DC 20) to enter a meditative state. This can allow the character to ignore fatigue or exhaustion for one hour, after which the character must rest, or make the skill check again. Characters without the Meditation feat take a –4 to concentration skill checks made for meditation. It takes ten minutes (100 rounds) to enter a meditative state.
New Use- Zen (this use of the concentration skill may not be used untrained): A character trained in concentration can tap the power of his Ki, focusing on the task at hand to the exclusion of all other considerations. Rather than attempting an action defensively, a character may make a concentration skill check (DC 20) to focus on it, gaining one of the following benefits: a +2 to his next check with that skill, take 10 in a stressful situation, or perform an action that normally takes 1 minute or less in a single round. Only one of these benefits may be applied to a skill check at a time. Characters without the Zen feat take a –4 on concentration skill checks made for Zen.
The character always suffers an attack of opportunity for this use of the concentrate skill, since he is ignoring all other considerations, including his personal safety, to focus on the task at hand. However, this attack will never reduce the character’s ability to perform his skill check.
Goin along with these two new uses are two companion feats.
Meditation (General)
You are practiced at meditative techniques.
Prerequisite: Concentration 3 ranks
Effect: You may make concentration checks for meditation without a –4 penalty. You may also enter a meditative state in 1 minute.
Normal: Characters without this feat suffer a –4 on concentration skill checks, and take 10 minutes to enter a meditative state.
Zen (General)
You are practiced in the art of Zen.
Prerequisite: Concentration 3 ranks
Effect: You may make concentration checks for Zen without a –4 penalty.
Normal: Characters without this feat suffer a –4 on concentration skill checks for Zen.