From NSIS Wiki
Setup authoring tool with NSIS integration
Excelsior Installer is a free tool for creating installation packages for basic installation scenarios.
In general, it is an independent setup generator itself. But since version 1.8 this product provides NSIS integration, that allows one to use it as a GUI wizard for NSIS to ease NSIS learning curve and simplify basic project creation tasks.
To build the NSIS installation package you use the packager wizard of the Excelsior Installer and set up basic package options, like files to include, shortcuts, license agreement, splash screen image, default names for installation root and Start-menu folders etc. Then you use menu command File->Export to NSIS and get the complete scripts set to build your installation with NSIS compiler. The wizard is able to run NSIS compiler itself so you may test your installation right away and correct any settings.
After that you may edit your scripts to customize the package as necessary.
NSIS v2.40 or later is required.