Assuming we are talk about IPP 5.3.
I do not understand what is the problem? As far as I know, our JPGView MFC application (which part of IJL package) open 1 channel JPEG images exactly in the way you mention (converting 1 channel JPEG into 3 channel BGR image), please take a look on FileOpenDlg.cpp, function GetImageFromJPG().
BTW, I recommend you to migrate from IJL to C++ JPEG codec which is part of JPEGView application. The reasons are: that codec supports 12-bit Extended Baseline mode, 2..16-bit Lossless mode, is threaded and demonstrate performance benefits when is running on multi-core system, is available for Windows, Linux and Mac OS X.