You can do part time diploma course if have minimum of 1year working experience in any domain but am sorry to say that there is no polytechnic college which allow part time diploma course without attending classes because its an technical course and you can't understand anything without attending classes.

Types of Diploma Courses
Diploma in Hardware maintenance
Diploma in Network Technology
Diploma in Electrical
Diploma in Computer Office Management
Diploma in Industrial Electronics
Diploma in Communication Engineering
Diploma in Computer Application
Diploma in Applied Electronics