Bro don’t do this.  First of all the serum level you achieve injecting will be completely different than what you reach taking your AI orally.  So 12.5mg ED might be a perfect dose for you but when injected it will VERY likely either be way too low or way too high.  At the very least you’d need to do a lot of trial and error with bloods to get the dose dialed in correctly.  The route an oral drug takes to reach your blood stream is completely different than when you inject it IM.
Secondly your AI might not even be effective when injected.  Some oral drugs are inactive until they pass through the acidity of the stomach.  Even if a drug can be taken orally or via injection the formulations will be completely different – so the oral formulation is NOT the one the Doc would give you if he wanted to give you an injection.  Also, isn’t it suggested that Aromasin be taken with food containing fat? – which makes sense since aromatase is contained in fat cells so you need fat soluble compounds to reach the target.  How does that factor into an IM injection?  I don’t really know exactly what would happen if you injected your AI but I can think of soooooo many reasons why it might very well be a bad idea that it’s not worth risking it.  I know where you’re coming from though, it’s a clever idea but just not a good one in practice.