Cricket rules to counting runs after win the match

The "easy" way to do this is via penalty runs:

1. The batting team commit an unfair action not otherwise covered in the Laws. Law 41.2 applies and the batting team's captain is told they've been naughty.
2. The batting team repeat the unfair action. 5 penalty runs are awarded to the bowling side, giving eight runs needed to win.

It's now trivial for both batsmen to score a century. Without penalty runs, it is not possible for both batsmen to score a century.