loadin and 5.1

[Tim Channon <tc@...>]

I'm trying to find a simple fix for Lua so that I can approximate user
edited sources as valid Lua source. (advice of use Lua as the config
file format but I need to avoid the difficult keyboard typing, can if
necessary add a more complex text top and tail during loading)
<preamable><user><postamble>

Guessing, 5.2 can do

M={}
loadin(M, something)

Making the external Lua local to M avoiding name crashes.

Is there a sane simulation of this in 5.1?