Reading user parameters: Is there a way to read user parameters for the user who is is currently logged on?
Yes, you can use the Include contained in our Tips&Tricks Nr. 20 and then, for example, work with "&V[user_parameter_BUK]" for the user parameter BUK.

An alternative, but less convenient, is to use a separate step in your InputScript that calls up a standard transaction where the user parameter is shown as the initial value in one of the entry fields.