IAPs are not configurable in this manner so IAPs are out.
You would have to use controllers, and use APs that have external antenna connectors (AP-204/214/224, etc). When you provision the AP, you would have to put them in to 'Single Chain Mode' (the user guide will identify which antenna ports should use (usually ANT0).
Your DAS/Leaky Coax will have to have integrated combiners/de-diplexing hardware (the APs output from theconnector both 2.4Ghz and 5Ghz on the same connection, so your DAS solution will have to split those into the 2.4Ghz and 5Ghz). If the DAS system doesn't have that, you will HAVE to use AP-228s or AP-274s.
Note that when you use Leaky Coax/DAS with WiFi, especially with 11ac APs, the following conditions/caveats must be acknowledged:
1. With single-chain, you will get no MIMO capability, and only the lower/lowest MCS rates (max throughput likely around 20-35Mbps in a real environment
2. You must disable ARM and statically set all the channels on all your APs manually, all leaky coax solutions have specific cables that are tied to specific channels.
3. You will not be able to leverage any type of wifi locationing service (thing like putting wifi users on a map).
4. It is a best practice that when installing the APs into the closet where the Leaky Coax is terminated, that all APs be placed into a shielded enclosure to minimize AP to AP interference and ACI (this adds a significant cost).
5. You WILL have hidden node issues, which can further reduce performance if the coax runs are long.
6. Coax installations are extremely susceptible to non-wifi interferenece (if you have a 200ft long run of leaky coax and a microwave goes off at the far end, every client on that run will be affected, even if they are 200ft away).
So it's really up to you if losing all of the above is worth using the leaky coax solution, or if you want to do a traditional wifi deployment for 11ac and reap all the benefits, and use the leaky coax solution for your cellular spectrum.