There are a few methods that would surely do help with indexing,
For a few couple/dozens of links, social sharing & blog comments in frequently-crawled websites/pages could do the work,
Other than that, you'll gonna need to automate things (warmed up news website, blog comments, etc...) or simply do pay for a service that actually does the job (none of the well known does actually work decently)
Although, it's all up to the kind of links you're trying to index,
LQ & spammy links do usually barely get indexed or/and get deindexed after a couple of weeks