DM_Fisk's Princes of the Apocalypse Campaign
Train to Gain levels
Instead of the variant rule listed in the DMG (levelling only happens after training) character may instead spend gold for exp through training.
To do this, the character must cover the cost of a moderate lifestyle for the time period plus the listed training cost, they may then exchange 1gp for 1exp.
This option can help players who miss sessions to catch up, or for characters that are ALMOST to the next level to reach it.