You are going about this in the wrong way. This "Go big or go home, I don't want to do a test dose" mentality is going to get you killed. Especially when dealing with high-potency Opioid products like Fentanyl patches. I'll start with the basics, Micrograms are 1/1000th of a Milligram not 1/100th so just keep that in mind. 7.5mg of Fentanyl would likely be a lethal dose for someone with your usage patterns.
There are really a variety of ways to ingest Fentanyl patches man, but none of them are going to be considered safe. It's difficult to extract the active ingredient from the patches while maintaining knowledge of just how much of the drug is contained in how much of the gel.
I think what you should do is use the Fentanyl bucally. Put a small piece in your mouth and treat it like you would a piece of candy or something. Keep it tight against your cheek, move it around, expose it to all corners of your mouth, remove the fragment of patch, then wait about 15 minutes to make sure you haven't overdone. From here, you should titrate your dose slowly and with caution.