A lot depends on what you are actually trying to achieve here.
Is it just Callbacks, or all Interactions? My guess is that you want your Agents to answer Live Calls and only if they don't have any for 2 minutes start processing callbacks? Unfortunately, this isn't how Callbacks were designed since they are intended to "hold you place" in the queue. It may be possible, but I can't think of a way to do it.
If it's all Interaction types (or the Agent only processes Callbacks) then you could use the ACW settings for the Queue to enforce a 2-minute "cool-off" period.
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Paul Simpson
Views expressed are my own and do not necessarily reflect those of my employer.
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