Timoteo becomes nothing more than a means to an end because although he is aware of the scheme to make Lucrezia sleep with another man he does nothing to stop it and instead seeks to benefit from it. To clearly understand his role we should take a look at the sequence of events leading to the deception.
Callimaco the young Florentine was determined to sleep with Lucrezia despite the fact that she was married. Callimaco sought the help of a marriage broker Ligurio to enable him achieve his objective. They then scheme to deceive Nicia who is Lucrezia’s husband by taking advantage of his wish to have a child. They convinced him that a potion from the mandrake root if taken by his wife would help her get pregnant. The catch was that the first man to sleep with Lucrezia after she ingests the potion would die so Nicia should allow another man to sleep with his wife.
Nicia accepted this plan and informed the wife but the wife needed to be convinced and this is where Timoteo a friar asks Lucrezia to take the potion and sleep with another man. Timoteo is paid by Callimaco and Ligurio using Nicia’s own money to set aside his moral obligation and participate in this scheme. Nicia accompanied by Timoteo disguised as Callimaco kidnap Callimaco who is disguised as a lute player and take him to sleep with Lucrezia. He becomes a means to end because he is aware of the deception but does nothing to stop it and instead supports the plot for monetary benefit.