I think ultimately using a lookup table would be the best option, so that we definitively get rid of sumtcita in the logical form.
Moreover I don't think we can handle all the sumtcita the same way. If {broda ba xy} implies {lo nu broda cu balvi xy}, can we infer that {broda seka'a mi} implies {lo nu broda cu klama mi}? I don't think so.
A sumtcita ↔ bridi relative clause conversion table could look like the below:
SE ba X = xoi ke'a SE balvi X vau
se pi'o X = xoi X se pilno fi ke'a vau
SE ka'a X = xoi fasnu fa ke'a jo'u lo nu X SE klama vau
fau X = xoi fasnu fa ke'a jo'u X vau
(Here {ke'a} stands for the outer bridi.)
Furthermore, {ba} and {pu} are irregular sumtcita, in that their underlying predicate is inversed when they're used with {bo}:
• { brode .ije ba bo brodo } = { brode .ije ba lo nu go'i cu brodo } (irregular ba/pu sumtcita)
• { brode .ije ki'u bo brodo } = { brode .ije se ki'u lo nu go'i cu brodo } (regular sumtcita)