Seems odd doesn't it?...I thought the same thing when I bought my bike..."Really? a Goldwing class motorcycle and they didn't think it thru to have a section where the wires can exit the cubby and have the lid closed!"
I use my adaptor mainly to power my gps unit...what I did was add another small hole next to the one I made to install the adaptor, so now I can plug in my dc adaptor and then have the wire feed right back out of the cubby thru the smaller hole...you can reach a hand down the left handle bar area and reach under the fairing until you can get hold of the wire....then just pull out what you need.