It is a bit more complicated than just controlling temperature for stability even for PWW resistors, TCR is only one parameter, aging is another and is affected by various factors such as temperature, operating parameters such as how much power is applied and for how long, how often. Drift is considered an uncontrolled parameter as such mainly because it depends on both internal and external factors that are not under control by the manufacturer. It also depends on the type of resistor (and no hermetic sealing does not eliminate all factors, it helps minimize external factors and can slow down internal factors to some degree), is it PWW or film/foil, ratings, type of construction, its intended purpose and has it gone through a PMO (post manufacturing operation, otherwise known as thermal shock and any other operations deemed necessary).
There are many grades of resistors, from commercial jelly bean one cent per to the primary standard types such as the SR-104 which cost accordingly as to specifications. There are no free lunches, you aren't going to get a transfer grade resistor out of a $2 or $4 resistor or for that matter even $20 or $30, those are not intended to be such and no matter what one does to them, will never achieve the same specs as a transfer standard resistor which is designed for the purpose. You aren't going to make an SR-104 out of a sow's ear no matter what you do, if it could be done, it would have been done already. Somebody is going to argue that somehow someone is going to do it, well have at it but don't bet the farm on it, remember such performance must be verified by a proper calibrated resistance system not some jury rigged mess on a table top, sorry, that is just the way it must be. You can't verify parameters if everything is moving around at the same time. In fact, someone else capable of verifying said performance should do it independently, again on a certified calibrated system of sufficient accuracy; no DVMs need apply here.
Could you possibly build something like a Fluke 752, yes with the proper parts but don't expect to get actual 752 performance without getting the correct parts, otherwise you are going to fall short of the target. There are many parameters to be determined for such a project, some of which many people are not aware of. If you want to play with PPMs, you're going to have to do it the right way or you're really just wasting time and effort.