Wa alaikum assalam, I would like to start answering this question in a non-conventional way, so kindly bear with me. The first thing that drew my attention in your question was the use of the word “extra” when referring to acts of worship. So my first advice to you is to thank Allah SWT for the spouse’s already practiced acts of worship, and to do this very sincerely with the following intention in mind:
And remember when your Lord proclaimed: If you give thanks, I will give you more (14:7)
The above is not by any means an invitation to accept the current situation, on the contrary, it’s a gentle way of knocking on Allah’s door by first thanking Him for what He has already blessed us with, for He has promised us to increase His favors “if” we are grateful for what we already have. The second step is obviously to preach and advise the spouse for their own sake. Having said so, it is highly recommended to preach in an “indirect” way so as to avoid offending them and losing their interest in the matter altogether. For instance, one may start a discussion with their spouse about their own fear and concern over their own death, and whether they are prepared for it or not, bearing in mind that it could take place any moment; consequently, one may suggest that they would like to offer a little more voluntary prayers, additional supplications, charity, etc. without referring to the spouse in any way. The prophet SAW said:
The remembrance of death is one of the means of showing humility before Allah; and that whoever seeks the Hereafter will abstain from worldly pleasures [Al-Tirmithi]
In another discussion, one may reflect on the beauty of this religion and how it is a middle way and a justly balanced faith, where one is “not” recommended to seek extremes, but rather to do those acts, which can be performed with ease and consistency, for the prophet SAW said:
Your duty is only to perform deeds which are carried out easily. By Allah, Allah will not withhold from you until you give up. The most beloved religion to Allah is one which is performed regularly [Muslim]
Other discussions may cover topics such as how Merciful Allah is on all of us, and how He SWT would accept from us even the slightest effort “provided” it is performed with sincerity and consistency, for He SWT said:
We have not revealed the Quran to cause distress (20:2)
Allah intends for you ease, and He does not intend for you difficulty (2:185)
Finally, one should make a “lot” of supplications for their spouse and for themselves, that Allah SWT increases their faith, purifies their hearts, and help them reach and remain steadfast on His straight path.
May Allah SWT guide every Muslim to what He SWT pleases.. Ameen..
And Allah knows best…