It's best to get the specific instructions from some senior ChNN student who does this practice and is very familiar with it. I do serkyem dharmapala practice according to the Dudjom Tersar, so my knowledge may be misleading as each lineage may have various specific instructions that could even be in contradiction to instructions in another lineage.
For instance, according to ChNN's ganapuja instructions, one takes a bite out of each food object one will offer in the remainder plate. In the Dudjom Tersar, one would never take a bite out of the remainder offerings, in fact they are set aside in the beginning when one first receives the tsok and kept clean.
That is just an example, to show that something that could be construed as a general rule between sibling lineages may very well NOT be a general rule!
So when it comes to making serkyem offerings to the Dharma protectors, this is serious business. I wouldn't fumble around as mistakes can have some kickback. Wait until you get 100% clarity from a senior practitioner in this lineage who is very familiar with the practice before you go ahead and try it.