The 21-year-old's contract with the Saints has expired after he joined on a four-month loan deal in August.
His time in Perth has been hampered by injury but Saints manager Steve Lomas said: "I'm grateful to Craig Brown for agreeing this. I can understand that he doesn't want to commit to anything beyond that for the moment.
"It will be good to have Peter available for the two games."
Saints host Dundee on Wednesday and - following the SPL's winter hibernation - travel to Motherwell on 20 January.