The following is arguably a little better, in that instead of clearing everything currently in the error frame it will just disable error reporting (and error sounds) when attempting to use the gloves:
Code:
/castsequence reset=target Hand of Gul'dan, Corruption, Dark Soul: Knowledge, Hand of Gul'dan, Metamorphosis, Doom, Doom, Grimoire: Felguard, Felstorm
/run SlashCmdList.UI_ERRORS_OFF()
/use 10
/run SlashCmdList.UI_ERRORS_ON()
/petattack
("/use 10" attempts to use whatever item is equipped on your hands; you could just as well enter the whole item name, except then this macro would be over the limit of 255 characters.)