Here are some things Ipulled before I fully tamed my ol lady
Fake a break down - I suggest this instead of ruining your 700. Just tell her your tranny went bad...
Make her car break down (again a fake). have her tranny "go bad". Then buy a new one (one for your rig) and pretend to fix hers when she is not around. then swap yours and never tell her about it
My wife has no problems shelling out cash to fix her car lol. But mine on the other hand, gets a conversation about why I need to fix it... So I used to just make hers break down so I could buy my parts with out a fight

She would say, my car is acting up. I'd say, it needs a new carb, I'll get one tomorrow and put it in. She gives me a huge thanks and "other favors" for being there to save her lol
Surely you will have problems with these since you made two huge mistakes for a rig builder.
First mistake - Never let the woman control the cash. You have no way of excluding her from purchases when she knows whats going on with the pay checks.
Second - Never tell her any specifics about your rig. She just may listen and notice when you buy something new.
I learned this from my dad. He once purchased a joiner for $500. He put it in the garage with all his other tools under a blanket for a couple weeks. He said he will take off the blanket later and she will think its been there the whole time. It worked

All she sees is a sea of tools and has no idea what they are or when they showed up. He did this with a band saw too. He said he would just say it was out in the shed and he dragged it in to the garage if she ever noticed.
If she does not know what you have, she will never know what is new...
I no longer do any of that. I just do it and if she has any trouble with it, that is her problem

Al she can do is leave me... Thats a win win situation lol