There is an old Oracle blog which mentions this. Don't know if it is still applicable or relevant to your case or not though:
Self-Contained Applications: Select Java Runtime to bundle
Packager tools in 7u6 assume current JDK (based on java.home property)
is the source for embedded runtime. This is useful simplification for
many scenarios but there are cases where ability to specify what to
embed explicitly is handy. For example IDE may be using fixed JDK to
build the project and this is not the version you want to bundle into
your application.
To make it more flexible we now allow to specify location of base JDK
explicitly. It is optional and if you do not specify it then current
JDK will be used (i.e. this change is fully backward compatible).
New 'basedir' attribute was added to tag. Its value is
location of JDK to be used. It is ok to point to either JRE inside the
JDK or JDK top level folder. However, it must be JDK and not JRE as we
need other JDK tools for proper packaging and it must be recent
version of JDK that is bundled with JavaFX (i.e. Java 7 update 6 or
later).
Here are examples ( is part of task):
<fx:platform basedir="${java.home}"/>
<fx:platform basedir="c:\tools\jdk7"/>
Hint: this feature enables you to use packaging tools from JDK 7
update 10 (and benefit from bug fixes and other features described
below) to create application package with bundled FCS version of JRE 7
update 6.