Shots boss Dean Holdsworth told BBC Surrey: "He wants to enjoy his football again. He's got a hunger to come back here and prove how good a player he is.
"He was a fans' favourite here once and he's another dimension to what we may need - Tim will be used."
Sills joined Stevenage from Torquay in January last year, but only made two appearances for their first team this season.
He spent three months on loan at Rushden & Diamonds during this campaign, scoring once in 11 games.
Holdsworth added: "I looked at the squad when I came in and there are a lot of players who are much the same size.
"My tactics change during a game. We can hit him as a target man, use him in a two or on his own.
"I'm delighted to have Tim with us. I'm hoping he proves he is a good signing."
Source: BBC Sport
Source: BBC Sport