Seeking advice, alternate trailer wiring plug

[CaptainPalapa]

We have the typical side-of-the-truck-bed fifth wheel plug on our F-350. (I didn't install it, but I definitely use it!)

I need to have an *additional* outlet down at the bumper. (Have to pull a "regular" trailer next week.) That trailer is also a 7-blade, so I bought a split 7-blade/4-flat outlet (because you always need the 4-flat). Can I just "tap" into the wiring on the other plug for it? (Heat shrink, all that, yeah.)

Not sure what other way I'd do it, but I'm betting someone out there has done this before. Any advice welcome.

Note: This is not for trailer-behind-another-trailer. This is to have an alternate socket at the bumper.