The most important diference is that the "small" and "tiny" versions
are compiled without the +eval feature. A possible solution takes
advantage of the fact that in -eval builds, the :if .. :endif complex
statement becomes a nestable comment: so if you add "if 1" at the
start of your vimrc and "endif" at the end, everything in between will
be ignored by the "small" version.
If that seems too much for you, you could write at the top a few
unconditional statements compatible with the "small" version (see
:help +feature-list and use only features preceded by S or T) then
after that write "if 1" alone on a line, any statements to be
interpreted only by builds compiled with +eval, and finally "endif",
again alone on its line.
Best regards,
Tony.