I can see a possible use case for a "mass pay" feature, but that does not really solve the problem here, where slush is generating a bunch of free transactions.  The use of a mass-pay feature without paying a TX fee might result in creating a single transaction that is larger than the entire free-transaction area (27k).

You wind up with the same end result: stalled transactions.  The root cause of the problem is that the pool is generating a lot of work for the network, without paying for it.  This is called Tragedy Of The Commons, or less graciously, free-loading.

So, I would support the following tweaks,

• Convert 27k free-TX area to purely score-based, eliminating 4000-byte limit
• Make -limitfreerelay the default
• Add a mass-pay JSON-RPC method, provided that the user interface requires a TX fee parameter (NOTE: zero is a valid TX fee)
• Reduce dust-spam/fee triggers from 0.01 to 0.001