You could use a Client Script to achieve this. In your code for your client script you could decide to show or hide the checklist variable based on some condition, i.e the Item is X and the Task is Y. Once you specify which Task you want to trigger it on you could then call the following code to make sure that the variable doesn't appear.
g_form.setVisible('variables.YOUR_VARIABLE_NAME', false);
To make sure you are only triggering the Client Script for a specific Item you can use the 'Item' field on the Requested Item table to check if it is a certain value. Since you are doing this on the SC_TASK level you will have to validate the item using some form of dot-walking to the Requested Item. As for figuring which Task to trigger it on, you will need to define how you identify the Task to trigger it on first then write that into your conditions.
Hope this helps.
