You'll have to re organize your schedule I'm afraid. A weekend in Vientiane really isn't something one doesn't have time for. You can always fly there if time is short. Spend a night or two then fly back.
Firstly why not just spend a couple of nights in Vientiane? It's a fantastic place and you'll find food and experiences you will either struggle to find in Thailand or simply can't be found here.
Secondly, if you did have to do a quick turnaround, then just cross the border and come straight back.
Vientiane is 20km from the border crossing (technically, it's on the border but you can't cross there, you have to travel to the friendship bridge).
This takes half an hour or perhaps 40 minutes during morning or afternoon rush hour.
There's no point in spending the night near the bridge on the Lao side. Aside from probably not having any lodging available (I don't remember seeing any) whatever might be available is for locals and unless you speak Lao or Thai and can read the language, you'll struggle to make yourself understood in such places.
99.99% of falang head into town, where hotel staff can usually speak decent English. There will also be transportation available, which won't be the case if you were to spend the night in some dingy dive 3km from the border (if it's even available as mentioned).
I heard immigration prefers 500K in a Thai account and might deny your application if it's in a foreign account or send you on a wild goose chase demanding authenticated bank statements and so forth.