Such languages tend to be reasonably smart about what changes trigger large recompiles, and about not re-parsing the same lines of header-only code over for every compilation unit. In C++ the best you can hope is to set up precompiled headers and live with the artificial dependencies.
If the only problem you have with header-only programming is compile times, might I humbly suggest that the problem you are actually concerned about is entirely somewhere else (hint: most language compilers are terribly unsmart about what changes trigger recompiles, as the cost of compiling the entire source tree isn't too terrible).
