There's really no substitute, period. Using the antacid can help with the amount of sn that your body can absorb, due to it lowering the acid in your body, thus less of the sn is turned to nacl(table salt). But as for an antiemetic, you definitely need it if you want to have the highest chance. Depending on where you live, it may be easy to obtain. In the USA(Where I live), it's prescription. The antiemetic will help your gastric emptying(more sn eventually gets into your blood), and most importantly, it will help you to not vomit. These things are a must for a high success rate.
Don't do tape on the mouth, as worried_to_death said. You'll suffocate on your own vomit. Even if you manage to swallow it(yuck!), you'll probably puke again.