The amount of open space/oxygen in a bin complete full of grain is absolutely MORE than enough to support a population of bugs for quite some time. By the time they've come even close to using the oxygen that is available to them, you already have a serious problem. Just ask anyone who has open an airtight cereal container to discover that weevils have taken over the joint. And there's a huge difference between purging a container with CO2 (which is all that's required to achieve the purpose we're talking about) - and pressurising a container with CO2. It's extremely easy to purge a container with CO2, not necessary to pressurise it - just displacing the oxygen in the container and creating a seal is enough.
The fact is that you don't need 100% CO2 in there for it to be virtually un-inhabitable for aerobic creatures, as CO2 is toxic to us all at much lower concentrations. At 1%, we become drowsy, 2% concentration is enough to cause confusion, laboured breathing & mild blood acidosis in humans when exposed for a few hours. 5% is toxic to us over a reasonably short period of time, and concentrations of 7% or higher will result in death sometimes within minutes of exposure.
This is the reason we are all so careful (or should be) with our CO2 bottles, and placement of them and checking that they don't leak/turning off the bottle when not in use if we're not sure about it. AREN'T WE. ......Because CO2 kills. If you don't believe me, start a leak in your CO2 gas bottle and go to bed. Chances are you won't be with us before the concentration in your home reaches 10%
So all you really need to do (if you really need to do anything at all except make sure the bugs can't get in in the first place) is give your bin of grain a decent shot of CO2 and close her up. If you have achieved 10% CO2 concentration, I think you can safely say that most bugs/aerobic organisms are going to be having a damned hard time - the last thing that will be on their minds will be mating
Having said all that, I think the whole excercise would be pointless, & an completely un-necessary expense.