But, if you need to, yes you can parallel the required temperature compensating capacitors across the main tuning cap to get the desired effect. In the old days, it was not uncommon to put a small lamp or wirewound resistor as a heat source to maintain the vfo circuitry above ambient, thus negating the need for temperature compensation. A temperature of about 20-30 degrees above ambient is usually satisfactory. You have to measure the drift of the unit across time, and figure out how much to add based upon that drift. I don't have the numbers right off.
Most folks do it the hard way and just add some and try it, add more if needed, etc.
You can make similar arrangements using a bimetal strip or small springs that will move small aluminum plates as changes occur with temperature. Use a small heat source to add sufficient heat to the unit to overcome differential losses due to ambient drift properties. That is why xtals have ovens and military vfo's are often built with heating ovens around the VFO part. It really does not require much heat, but it does require a constant heat and a constant heat flow out of the VFO into the surrounding environment, such that any local changes in the environment are swamped by the outgoing heat from the vfo and thus effectively negated. In my RMCA rig that heating element was a small wound nichrome strip that ran off the filament voltage and added a couple of watts of heat to the vfo compartment.