A little reading through the developers documentation would have solved the problem.
Block.io eases your burden of storing information regarding users' addresses, labels, and user IDs. Below, we provide various methods that allow you to make fine-grained withdrawals from your account(s). You can withdraw from any addresses, from specific addresses, from specific user ids, and from specific labels, and you can send the specified amounts to up to 2500 destination addresses, users, or labels in a single API call.
The amount withdrawn must at least be 2 DOGE, 0.00002 BTC, or 0.002 LTC. Please keep at least 1 DOGE, 0.0001 BTC, or 0.001 LTC for network fees. There are no Block.io fees. Larger transactions (in bytes) will incur larger amounts of network fees as per Bitcoin/Dogecoin/Litecoin specifications. As of 06/09/15, you can now specify an additional parameter priority={low,medium,high} to increase the network fee paid in the given transaction. More specifically, priorities of low, medium, high will pay 1x, 2x, and 5x the minimum network fees possible on the network, respectively. As of 07/07/15, network fees will auto-scale according to network loads if the priority parameter is not provided.
So you can use the code :
/api/v2/withdraw/?api_key=API KEY&amounts=AMOUNT1,AMOUNT2,...&to_addresses=ADDRESS1,ADDRESS2,...&pin=SECRET PIN {additional paramter goes here}
priority=Low