A very easy option would be to compile QtCreator from source and change the naming rule in file
/plugins/cppeditor/cppquickfixes.cpp. Search for class GenerateGetterSetterOperation. In the constructor the variable name m_getterName and m_setterName are defined here.
The piece of code you are looking for is:
m_getterName = m_baseName != m_variableString
? QString::fromLatin1("%1").arg(m_baseName)
: QString::fromLatin1("get%1%2")
.arg(m_baseName.left(1).toUpper()).arg(m_baseName.mid(1));
m_setterName = QString::fromLatin1("set%1%2")
.arg(m_baseName.left(1).toUpper()).arg(m_baseName.mid(1));
You have to change the first part to something like:
m_getterName = m_baseName != m_variableString
? QString::fromLatin1("%1").arg(m_baseName)
: QString::fromLatin1("%1%2")
.arg(m_baseName.left(1).toLower()).arg(m_baseName.mid(1).toUpper());
Honestly, i did not check for correctness.
EDIT: Hyde is absolutely right. I did not check the mechanism that i cited in-depth due to time limitations but tried it a few minutes ago and checked the source.