The Make VB6 action always specifies /out <temp path>\vsmake.err for the output file. However, you could temporarily modify the TEMP environment variable before one of the Make VB6 steps. Add a Set Macro action to create a temporary TEMP macro to the desired path, checking 'add to environment variables...' option (the TEMP variable will be affected for that Visual Build process and any processes created in subsequent steps). The original TEMP env var value can be restored afterwards via another Set Macro action to delete the TEMP temporary macro/env var.
You may also need to create the alternate folder if it doesn't exist (if the VB6 compiler doesn't create it); you could use a Run Program step with a command of
%DOSCMD% md "drive:\path"
(and see this FAQ
http://www.kinook.com/Forum/showthread.php?threadid=46 for how to build that step only if the folder doesn't exist).