Edit: just so I preempt comments along the lines you know nothing about how IPS works, I will stipulate that, and instead direct my answer towards the general method of inspecting HTTPS traffic.
The short is answer is you can't.
The long answer is you would have to perform MITM attacks against the connections. This can be done in cases when you only have serverside authenticated HTTPS connections if you can force all your clients to trust a certificate that is under your control. It's often used but in my opinion it is a bad security practice since usually whatever certificate you use, will have lower guarantees of safety then the ones usually trusted by browsers and users. Even if it doesn't you are adding a new point of attack.
If you do have to use the MITM attack make sure you at least check that the certificates you are getting (from the servers) are correct, applicable for the serversm trusted and not on CRL's.
One other by-product of this approach is you are most probably teaching your users questionable security practices since they will be willing to trust obviously faked certificates for servers they communicate with. Then when they go to a hotel and see the same issue they might just assume that they are doing the same thing and happily divulge all company secrets over insecure connections.