To control the Pokémon and nature you get, you have to manipulate the PIDRNG. Make sure you're saved on B1F (there's no moving NPCs there, which makes things a lot easier), put your seed into the main window of RNG Reporter under the Gen 5 PIDRNG method, click Calculate Initial PIDRNG Frame, then click Generate. Find the first frame that is either Relaxed or synch-able (bolded nature) that has an encounter slot for Ferroseed (RNG Reporter has a list of encounter slots in the 5th Gen Tools menu), find out how many frames are between where it starts and your target, and save that many times (for instance, if it starts on frame 48 and the first frame with Relaxed/sync and an encounter slot for Ferroseed is 53, you would save 5 times) before using Sweet Scent.