I cannot speak directly for LTIB on the imx platform, but I have done some porting of packages not included in LTIB for the MPC8313E BSP.
For those packages I ported in, I've had various cases of an easy to port and hard to port case, but in each case, I had to create a custom .spec file based on taking examples .spec files from existing LTIB ported packages, and modifying them by hand and/or copying in sections from the .spec file from the package.
The two parts where I've had the most problems and things to work out are in the area of spec files in the prep and install portions of the spec file. This is due to the fact that packages compiled for PC/Linux platforms often have a lot of assumptions as to filenames directories to get, read and/or write into and assume that the machine the package is being built on is also the same it will run on. This is not the case in LTIB in that it has to build for a target machine, so simple things such as where the compiler/tools are, where the output has to go, where the .tar, bzip, gzip files are, etc. are different for LTIB versus a standard Debian, Fedora, etc. linux machine.
The other thing that can cause issues is the makefile itself in that it can have assumptions on the environment that are not the same in LTIB.
What I wound up doing for each package I ported to LTIB was take it on a case by case basis and also basically reverse engineer the build/install process of the package in combination with some trial and error to get it all to work. In each case however, I could not find a magic bullet to just set some enviromental variables and in each case I had to create a new .spec file and often had to also modify the makefile. The good news is once you understand how it works, it is a somewhat tricky task to get it ported, but it is not impossible.