It is not permissible to help a kaafir or a Muslim to buy alcohol or to do any other evil or sinful thing. The one who does that is a loser and a sinner. Allaah forbade that in the Qur’aan, when He said (interpretation of the meaning): 

“Help you one another in Al-Birr and At-Taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression”

[al-Maa’idah 5:2]

The Messenger of Allaah (peace and blessings of Allaah be upon him) cursed ten types of people with regard to alcohol. 

It was narrated that Anas ibn Maalik said: The Messenger of Allaah (peace and blessings of Allaah be upon him) cursed ten types of people with regard to alcohol: the one who presses (the grapes, etc), the one for whom that is done, the one who drinks it, the one who carries it, the one to whom it is carried, the one who offers itut, the one who sells it, the one who consumes its price, the one who buys it and the one for whom it is bought. 

Narrated by al-Tirmidhi, 1259; Ibn Maajah, 3381. This hadeeth was classed as saheeh by Shaykh al-Albaani in Saheeh al-Tirmidhi, no. 1041 

So whoever drinks alcohol or helps someone else to do so deserves the curse narrated in this hadeeth. So it is not permissible for you to help anyone to drink alcohol or to commit any other haraam action. 

And Allaah knows best.