It's going to be very difficult to brute force that... block.io generates MultiSig addresses using a combination of the 12 word mnemonic and the "secret PIN". So, attempting to use something like the "seedrecovery" script in btcrecover will not work, as it will not be able to simply convert the mnemonic "guess" to a seed and then generate an address from that seed and compare to a known address...
![Undecided](https://bitcointalk.org/Smileys/default/undecided.gif)
So, you would need to manually create all the valid seeds possible using your "11 words" as the base... then manually "test" the values in the "Settings" page to try and change the secret PIN.
I had a quick look at the brute.bip39 tool, and while it will generate valid BIP39 seeds... it doesn't generate only 180 valid combinations. Because you only have a 12 word mnemonic (instead of 24 words) it ends up generating somewhere in the 1400-1600 range of valid seeds!
![Shocked](https://bitcointalk.org/Smileys/default/shocked.gif)
... so that is going to take a while to work through, but I would say that it is certainly doable in a few days/weeks
![Tongue](https://bitcointalk.org/Smileys/default/tongue.gif)