Converting @user3306356's comments into an answer here.
One possibility is
摎 | lau. This is reported by moedict and Minhakka as only 和/跟, but maybe it can be used (@user…) seems to think so) the way I asked for. He reported the following examples:
Kung-nyin yung shȧk-tshàm lau sìi khat tshoi shȧk-pi tang.
Workers carve characters on steles with carving tools.
Kim-pu-nyit hà-pan yi-tshiên, yit-thin òi lau thien-kwong-nyit khoi-fù kài tsii-liàu cún-phì háu-shè.
Before I stop working today, I will surely prepare the resources with which I'll attend a meeting tomorrow.
This use is confirmed by both the above-mentioned dictionaries for his "better bet"
將 | tsiong, which is used this way in Mandarin too.
I will ask confirmation from Hakka speakers on the Facebook group Hakka Verse about these usages.
@user... commented on this answer with this, which has one of his example. Weird that the same dictionary giving this as an example for another word fails to mention the usage of
lau in said example in the article about
lau. Anyways, I guess that is confirmation of the usage. Hakka Verse hasn't responded yet.