Actually the UV transmission through some enlarger lenses and also some process lenses is not terrible. But in addition to those losses, if you did install a specialized UV bulb, then when you enlarged, you'd looking at very long exposure times due to inverse square losses. Notice how bright ordinary enlarger bulbs have to be in order to overcome this, just with visible light; getting that kind of luminosity in the UV is expensive, I guess you might be forced to use a mercury or deuterium lamp with Uv mirror to focus the light down, or such. Anyway, notice that in a UV exposure system the neg and paper are held very close to the light sources- it is for this reason. So probably only for really small enlargement factors would this be practical.
If 4x5 strikes you as too small then you could enlarge to another negative, or scan to a digital neg, or scan to an LVT. Either way you will be able to get a contact-printable negative.