If stretching the spring won't work, ge a brake noodle from a V-Brake:
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Or, if you have access to it, that thin hydraulic brake line.
Cut it to size & route the cable through that. Hopefully (maybe with the help of some hardware fitting, like a cupped washer) it'l hit the spring and act as a spacer.
BTW: Its supposed to take great deal of force to pull that arm. If you can do it with your thumb, you're good. Seems almost like the delicate arm would break, but it doesn't. Too loose and it won't go in gear all the way. All that force you're feeling helps keep that wheel stuck to the clutch, or it would slip.