How to call a .rgs script with ExeShell?

The following console application "RegRGS.exe" that runs a ".rgs" file requires the phrase:

MODULE="$INSTDIR\some.dll"

Where there can't be any spaces and it must have doubles quotes.

How would you format a call to "ExecShell"?

ExecShell "open"
$INSTDIR\RegRGS.exe
$INSTDIR\ascript.rgs
MODULE="$INSTDIR\some.dll"

In other words, where would you put any single or double quotes?

The following does NOT work:

ExecShell "open" '$INSTDIR\RegRGS.exe $INSTDIR\ascript.rgs MODULE="$INSTDIR\some.dll"'

You should double quote where there is $INSTDIR too because it might have spaces in it.

ExecShell "open" '"$INSTDIR\RegRGS.exe" "$INSTDIR\ascript.rgs" MODULE="$INSTDIR\some.dll"'