Zillions of possibilities here. If I understand correctly, you are mainly concerned about the possibility that there is no obvious boundary between the subject and object in case there is a multiple of one or the other. But I do not see that as a problem at all:
1) Minimal marking by word-order
If the language requires subject, then it is fairly clear the first word is a subject. Then you have a transitive verb that requires an object, so know that the stuff before the verb is object. Bob Susan, John and Dan kicked is perfectly interpretable because the verb requires object, thus Dan is part of the object, then its pair noun John too. Now you know Bob is subject and you consider only whether Susan is subject or object. It is clearly object because if rules of pairing with and are similar to English, the and is always before the last element of the chain.
Considering that human mind does not favour long chains of elements on the same level (John, Peter, Susan, George, Nathalia,.... went to school.), it is highly unlikely that even this minimal marking by the word order itself would pose significant problems.
2) Prosodic marking
Syntactic units typically share also their own intonation/pitch contour. Thus it is likely that even with very minimal marking, the phrasing would be Bob | Susan John and Dan | kicked thus clearly separating the subject from object.
3) Syntactic restrictions
The position between subject and object may work like the weak position in many Slavic languages and attract all the clitics, thus separating the subject from the object. Connected with some obligatory particles (say Japanese-like topicality markers), this could pretty much work in every single sentence.
4) Overt morphological marking
Case endings, clitics, whatever your heart may please. Subject can have even zero-morpheme and it is the object that bears the marking (this is actually fairly typical).
5) Covert morphological marking
Congruence between the verb and either the subject or the object. I.e. in Bob Susan and John kicked, the verb would be conjugated for 3SG in case of congruence with the subject, thus clearly marking it is just the very first noun, or 3PL in case of congruence with the object.
6) Combo
Languages tend to be fairly redundant in conveying information in order to make sure it goes through even in case of noise in the channel, thus more/all of the above possibilities are likely to go together.
