I am able to run C:\QuickBuild\useragent\bin\agent start/stop without first being in the C:\QuickBuild\useragent\\bin folder.
However, when I try to run C:\QuickBuild\useragent\bin\config.bat, I get this error:

Exception in thread "main" java.lang.RuntimeException: java.io.FileNotFoundExcep
tion: D:\resource\release (The system cannot find the path specified)
        at com.pmease.quickbuild.bootstrap.BootstrapUtils.wrapAsUnchecked(Bootst
rapUtils.java:50)
        at com.pmease.quickbuild.bootstrap.BootstrapUtils.loadProps(BootstrapUti
ls.java:347)
        at com.pmease.quickbuild.bootstrap.Config.main(Config.java:26)
Caused by: java.io.FileNotFoundException: D:\resource\release (The system cannot
 find the path specified)
        at java.io.FileInputStream.open(Native Method)
        at java.io.FileInputStream.<init>(Unknown Source)
        at com.pmease.quickbuild.bootstrap.BootstrapUtils.loadProps(BootstrapUti
ls.java:343)
        ... 1 more

I can see in the script that you are trying to make this possible, but the _REALPATH is apparently missing from some internal reference.
By adding this line to just before the java line in the script, I can get it to work from anywhere:

pushd %_REALPATH%