This achievement is story related, so you can't miss it.
*** Spoiler - click to reveal ***After getting and you should have a signed contract and a Pony Express stamp.
Use the stamp on the signed contract and flush it to Hoagie.
Hoagie then goes outside to the mailbox, puts the contract in the mailbox and puts up the flag. A pony express courier will pick up the letter.
In the present, Dr. Fred will get a call that he got two Million Dollars on his Swiss number account.
In order to get make sure the stereo in green tentacle's room is still playing the loud music.
After getting you should know the number for the shopping channel and you can use the phone in the office with the safe.
With Hoagie's Chron-O-John operational after and Laverne's in Dr. Fred will pull the lever and unlock the achievement.