I also didn't think of this before you asked, and I'm not sure if Professor Lavelle has touched about the d-orbital and hybridization in class (I'm sure he will.) However, after researching the internet, I found that you DO place the d infront of the s and p orbitals as you would do given the molecule does not have hybridization of orbitals. So, using your example, it would be dsp^3. In addition, you can also place subscripts for the d orbital as well (E.g. d^2sp^3), for when you move up into higher energy levels, you can be more specific and properly identify the hybridization of the molecule's orbitals. As far as reasoning goes, I'm taking an educated guess that the same concept applies for placing the d-orbital before the s-orbital. When we get to the 4s and 3d orbitals, the lower energy level of 4s is filled first, however, after we begin adding electrons to the 3d sub shell, it becomes less in energy and so we express it as 3d4s. I believe with hybridization you do this as well because the energy levels remain the same(they might change in energy I'm not positive, whereas hybridization is more focused on which orbitals are expressed at that energy level. I hope some of what I said is right, but if others could weigh in it would help!https://www.youtube.com/watch?v=s7zpdYS6abo
Also, this video elaborates on the d-orbital if your curious, but doesn't explain why the d is placed in front.