As tachyon mentioned, nohup should work... I have used it before.. sample...

@lines = $t->cmd('nohup sleep 300 &');  
print @lines;              
@lines = $t->cmd('jobs');  
print @lines;              
$t->close;
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output:

[1]     6962                                    
[1] +  Running                 nohup sleep 300 &
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