You could possibly allow the user to choose a second directory that is used for that installer.
Do you author the chained installer yourself or just including it in your overall install?
Generally, if you add an INSTALLDIR= to the command line then that allows you to pass the parameters. You might try that with the chained installer - but running it outside of yours for a test. Make sure you can control where it installs to by passing in the INSTALLDIR= parameter and if that works then you should just need to set the same command line. If you cannot do a command line with a chained installer then just launch it as a nested installer.
Remember, chained installers are only supported by MSIEXEC.EXE 5.0 or later. If all of your customers are not on that level or cannot install that version of MSIEXEC.EXE for any reason then they won't be able to run your installer. The older way of nesting installers can work fine, too, and definitely lets a person pass the parameters.
Sorry, should have said MSIEXEC.EXE 4.5 or later for chained installs. Probably OK, just a caveat to note in case you have customers on the older operating systems.
