There appears to be no way of setting frictionless requests as on for facebook ios sdk. For Javascript inplementations this can be done in the fb.init method.
The on
Frictionless requests can be turned on by setting the "frictionless" parameter of the apprequests dialog to "1". For example;
// create a dictionary for our dialog's parameters
NSMutableDictionary *params = [NSMutableDictionary dictionaryWithCapacity: 7];
// set the frictionless requests parameter to "1"
[params setObject: @"1" forKey:@"frictionless"];
// ... add other parameters ...
// show the request dialog
[facebook dialog:@"apprequests" andParams:params andDelegate: nil];
I think this also answers Frictionless Requests on iOS - how?