No. Lightroom 4.x will never be able to open Raw files from the D810.
D810 support has only just been added to the RC version of Camera Raw 8.6. It is never retrospectively added into older versions.
Adobe will probably add D810 support to the next version of Lightroom.
Either way you'll have to upgrade to Lightroom 5 to be able to open D810 Raw files in Lightroom.
You can convert the D810 NEFs to DNGs using the DNG Converter 8.6 or newer. Right now the DNGC 8.6 release candidate is available at Adobe Labs in the ACR 8.6 CS6 set of files, and eventually, the final version of the DNGC 8.6 will be available on the Adobe Updates page: http://www.adobe.com/downloads/updates
LR 5.6 is available as is ACR 8.6 Final.