To be sure, SAS EG 6/7 can be installed in two ways :
1. using SAS Deployment Wizard and a SASDepot
2. with SAS EG independent installation package (~ MSI format ) See. appendix A in the reference below :
https://support.sas.com/documentation/installcenter/en/ikdeploywizug/66034/PDF/default/user.pdf
SAS EG independent installer can be found inside the SASDepot itself :
<SAS Depot root folder>\standalone_installs\
Either ways no. 1 & 2 can use silent installs with Response properties but neither (officially) can invoke environment variables storing installation paths, or something approaching which would answer your need like for instance :
SET SYS_VAR_HOME=<choose one>
setup.exe -install %SYS_VAR_SASHOME%
Usage no. 2 requires only one path (SAS_HOME) in its response properties. I suppose usage no. 1 also requires the SAS licence path.
Of course, you could also try to script some shell launcher that dynamically creates a disposable response.properties for each installation, taking the install path(s) as parameters , broadly like :
launcher_install_sas_eg.cmd, PS1 etc. <SAS_HOME>
:: launcher script
:: create response.properties
echo SAS_HOME=%1% > ...\response.properties
echo SAS_EG_MODE=32-bit > ...\response.properties
echo LANGUAGE_SELECTION=en etc. > ...\response.properties
:: run SAS installer based on previous response.properties
setup.exe -install ...\response.properties