IKEA Lack Leg joiner when one half or both are hollow

My ongoing Lack enclosure project has now started to focus on the E12 printer. The height of this enclosure is such that I wanted to utilise the cut down legs rather than print off 4 200mm extension pieces. There are many leg joining designs out there but I wanted one that would fit to the bottom of an intact Lack leg but enable a good stable fit of a cut-down leg which will have a hollow end rather than the glued in plug of the standard full length ones.
The design allows the fixing of the j