Actually there are ways of using a DLL CA in InstallShield LE. Check out my "Augmenting InstallShield" blog articles such as:
Augmenting InstallShield using Windows Installer XML - Certificates
The concept is you use Windows Installer XML (WiX) Deployment Tools Foundation (DTF) to author a C# managed custom action. (See more here: Deployment Tools Foundation (DTF) Managed Custom Actions ) You then author a merge module to encapsulate this custom action and it's sequencing information. Then finally you consume this merge module in InstallShield.