Look at Make's addprefix function.
Here is an example we use with addsuffix to place obj files one directory below
the source.
SOURCE += MainThread.cpp
SOURCE += Blah.cpp
OBJ=$(join $(addsuffix ../obj/, $(dir $(SOURCE))), $(notdir $(SOURCE:.cpp=.o)))
From the make manual:
http://www.gnu.org/software/make/manual/make.html
$(addprefix prefix,names...)
The argument names is regarded as a series of names, separated by whitespace;
prefix is used as a unit. The value of prefix is prepended to the front of each
individual name and the resulting larger names are concatenated with single
spaces between them. For example,
$(addprefix src/,foo bar)
produces the result `src/foo src/bar'.