You might be able to accomplish more or less the same goal by dual licensing under AGPL and paid proprietary if you require a contributor agreement. QT (a GUI library for C++) is dual licensed LGPL and proprietary because some corporate users are uncomfortable using LGPL software (LGPL allows software to be dynamically linked but not statically linked to proprietary code).
The reason why I suggest AGPL is because it closes the "running it on a web server isn't distribution" loophole in GPL and that makes AGPL code persona non grata at Google and most SAAS companies. This license scares many companies either because they want to modify GPLed code without sharing changes or because they're afraid of having to open source other code that the AGPLed code is integrated with. This would effectively be virtually the same as a non-commercial/proprietary dual license but you'd be able to rely on the Software Freedom Conservancy's lawyers to enforce your copyrights for you and you'd have the support of the existing FOSS community.
The key however is that you have to do the contributor agreement and secure copyright or an unrestricted license to all code before merging it into your project. Otherwise offering the proprietary license option would be copyright infringement on your part if any contributor objects because you'd only have rights to their contributions under AGPL. (It's also a good idea in general to make sure any employed contributor's employer isn't going to attempt to claim copyright to their FOSS contributions before accepting the pull request.)
The reason why I suggest AGPL is because it closes the "running it on a web server isn't distribution" loophole in GPL and that makes AGPL code persona non grata at Google and most SAAS companies. This license scares many companies either because they want to modify GPLed code without sharing changes or because they're afraid of having to open source other code that the AGPLed code is integrated with. This would effectively be virtually the same as a non-commercial/proprietary dual license but you'd be able to rely on the Software Freedom Conservancy's lawyers to enforce your copyrights for you and you'd have the support of the existing FOSS community.
The key however is that you have to do the contributor agreement and secure copyright or an unrestricted license to all code before merging it into your project. Otherwise offering the proprietary license option would be copyright infringement on your part if any contributor objects because you'd only have rights to their contributions under AGPL. (It's also a good idea in general to make sure any employed contributor's employer isn't going to attempt to claim copyright to their FOSS contributions before accepting the pull request.)