McShane has been sidelined with a foot injury and Fry has moved to bring in the 24-year-old for Wednesday's reserve match against Norwich City at London Road.
Gore has spent his entire career with The Dons but has not yet made a first-team debut for the South West London club.
With Posh number one Mark Tyler the only fit custodian at the club, Gore will assume the number two role during his spell with the Second Division outfit.
Meanwhile, midfielder Tony Scully will also appear in Peterborough's reserves on Wednesday in order to get some match fitness following his move to Conference side Dagenham & Redbridge.
Scully had joined The Posh on non-contract terms late last month before deciding to move to the Victoria Road outfit last week.
