Are you using products with ingredients that can be absorbed anyway? A lot of stuff does sit on the surface, you may be more prone to noticing build up having fine hair and currently using non water soluble stuff like cones. I used to get build up with commercial products (shampoo and conditioner, no stylers) even tho I have porous hair, my hair always looked good right after colouring because basically the dye clarified for me!! Pre-CG I used a 'light' spray conditioner that was little more than silicone in water, now I use a generous application of a rich cream one but no build up because everything is water soluble. I also notice different cationic surfactant bases give different effects when used as a leave in.

You could try using the conditioner as the emulsifier for the oil and water mix, but I would only make up a tiny batch unless you intend to use a preservative. Mineral oil won't feed microbes AFAIK, diluted conditioner absolutely could. IMO purchase a proper emulsifier like a polysorbate or a preservative.
2a-2c, medium texture, porous/ colour treated. Three years CG. Past bra strap length heading for waist.

CO-wash: Inecto coconut/ Elvive Volume Collagen
Treatments: Komaza Care Matani, coconut/ sweet almond/ fractionated coconut oils, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss Ultimate Volume, various Elvive
Styler: Umberto Giannini jelly, Au Naturale styling gelee
Flour sack towel, pixie diffuse or air dry.
Experimenting with: benign neglect