Here is one approach that might work. It requires some knowledge of block masking.
- Create a subsystem. Inside the subsystem, place a constant block connected to an output port. Set the value of the constant block to be "K"
- Mask the subsystem
- Edit the subsystem mask. Add 3 "Edit" parameters. 1 for the bus name, the second for the bus element name. The third should have the name "K" and uncheck the "Visible" box.
- On the mask "Initialization", add code that:
- Creates an instance of the bus specified in the first parameter
- Searches the bus to find the bus element specified by the second parameter
- Sets the workspace mask variable "K" created in step 3 to be the min or max value of the bus element