The word wishing is used as a participle in this sentence. Gerunds and participles look the same - they have the same form of adding the suffix -ing to a verb. However, their function in a sentence is different. Whereas gerunds are used as nouns, participles are either used as adjectives or as adverbs. In this case, <em>wishing </em>is used as an adverb (how did he ask the florist? - wishing to remain anonymous), which is why it is a participle rather than a gerund.
