The Ti PTR08100w is not a boost /buck regulator. It is considered a Buck regulator and has no boost capability. Ti does have boost/bucks but not in the module form like the 08100. So they are not as simple as just adding a couple caps and a pot.
The PTN04050C that sci pointed out is considered a Boost regulator. It is also in the module form so it is pretty simple to set up. People have got it to go lower then 5 volts by using blocking diodes that have a forward voltage drop. Not a very efficient , but it does get the job done.