After installing Photoshop Wireframing Kit you can easy add them to your current Custom Shapes
1) To use a new Custom Shape you've downloaded, you'll have to first select the Custom Shape Tool from the toolbar.
2) Now, from the Custom Shapes Options Bar, select the Custom Shape Picker dropdown. From here, you'll be able to pick any of your currently installed custom shapes for use in your documents.
3, 4) However, right now we want to ignore all of these shapes, and instead click the arrow on the right side of the picker. From here, we want to "Web-Design-Shapes..."
5) By choosing "Ok" you will add only Web-Design-Shapes and all your current custom shapes will be removed from the selection, by choosing "Append" you will add the Web-Design-Shapes on the bottom of your current custom shapes.