eOne now has SmartConnect Excel Data Entry Templates for Microsoft Dynamics GP 2013.
The eOne Dynamics GP and CRM Blog: SmartConnect Excel Data Entry Templates for Microsoft Dynamics GP 2013
Microsoft & the GP EcosystemExcel & OfficeDevelopment & IntegrationGP 2013
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.